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MySQL语句使用。

程序员文章站 2022-05-18 21:14:10
MySQL的DDL、DML、DQL语句和单表增、删、改、查 [toc] 实验准备: 1. 初始化设置过的centos虚拟机 2. 安装MySQL数据库 实验开始: DDL语句 1. 创建和删除数据库 2. 查询数据库字符集 MariaDB [(none)] show create database ......

mysql的ddl、dml、dql语句和单表增、删、改、查

实验准备:

  1. 初始化设置过的centos虚拟机
  2. 安装mysql数据库

实验开始:

ddl语句

表:二维关系 设计表:遵循规范
定义:字段,索引
字段:字段名,字段数据类型,修饰符
约束,索引:应该创建在经常用作查询条件的字段上
  1. 创建和删除数据库
mariadb [(none)]> create database testdb1;     (分号为结束符)
query ok, 1 row affected (0.00 sec)

mariadb [(none)]> show databases;  (列出所有数据库)
+--------------------+
| database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| testdb1            |
+--------------------+
4 rows in set (0.00 sec)

[root@centos7 ~]#tree /data/mysql/testdb1/   (其实就是在mysql下面建立了一个目录)
/data/mysql/testdb1/
└── db.opt

[root@centos7 ~]#cat /data/mysql/testdb1/db.opt (也可以查看里面的内容,字符集也可以看到)
default-character-set=latin1
default-collation=latin1_swedish_ci
0 directories, 1 file

mariadb [testdb1]> drop database testdb1;   (删除数据库,同时mysql下面的testdb1目录也会删除)
query ok, 1 row affected (0.00 sec)

mariadb [(none)]> show databases;
+--------------------+
| database           |
+--------------------+
| hellodb            |
| information_schema |
| mysql              |
| performance_schema |
+--------------------+
4 rows in set (0.00 sec)
  1. 查询数据库字符集
mariadb [(none)]> show create database testdb1;   (查看testdb1的数据库字符集)
+----------+--------------------------------------------------------------------+
| database | create database                                                    |
+----------+--------------------------------------------------------------------+
| testdb1  | create database `testdb1` /*!40100 default character set latin1 */ | (这里最后的为字符集既latin1这个字符集不支持汉字的。)
+----------+--------------------------------------------------------------------+
1 row in set (0.00 sec)

(这样也可以查看比较好辨认)
mariadb [(none)]> show create database testdb1\g;
*************************** 1. row ***************************
       database: testdb1
create database: create database `testdb1` /*!40100 default character set latin1 */
1 row in set (0.00 sec)

mariadb [(none)]> show create database mysql; (查看mysql的数据库字符集)
+----------+------------------------------------------------------------------+
| database | create database                                                  |
+----------+------------------------------------------------------------------+
| mysql    | create database `mysql` /*!40100 default character set latin1 */ |
+----------+------------------------------------------------------------------+
1 row in set (0.00 sec)
  1. 修改字符集
mariadb [(none)]> alter database testdb1 character set utf8mb4; (这个字符集支持全球文字还支持表情包)
query ok, 1 row affected (0.00 sec)

mariadb [(none)]> show create database testdb1;
+----------+---------------------------------------------------------------------+
| database | create database                                                     |
+----------+---------------------------------------------------------------------+
| testdb1  | create database `testdb1` /*!40100 default character set utf8mb4 */ |
+----------+---------------------------------------------------------------------+
1 row in set (0.00 sec)

[root@centos7 ~]#cat /data/mysql/testdb1/db.opt   (文件也会修改)
default-character-set=utf8mb4
default-collation=utf8mb4_general_ci
  1. 创建一个表做实验
mariadb [(none)]> use testdb1;
database changed
mariadb [testdb1]> create table test ( id int unsigned auto_increment primary key,name varchar(10) not null,mobile char(11) not null );
query ok, 0 rows affected (0.01 sec)

mariadb [testdb1]> desc test;   (查看表结构)
+--------+------------------+------+-----+---------+----------------+
| field  | type             | null | key | default | extra          |
+--------+------------------+------+-----+---------+----------------+
| id     | int(10) unsigned | no   | pri | null    | auto_increment |
| name   | varchar(10)      | no   |     | null    |                |
| mobile | char(11)         | no   |     | null    |                |
+--------+------------------+------+-----+---------+----------------+   
3 rows in set (0.00 sec)



mariadb [hellodb]> show tables;   (列出当前库里的所有表)
+-------------------+
| tables_in_hellodb |
+-------------------+
| classes           |
| coc               |
| courses           |
| scores            |
| students          |
| teachers          |
| toc               |
+-------------------+
7 rows in set (0.01 sec)

(查看表内容,先要进入存在这个表的数据库)  这个表是我从外部导入进来的没有手工创建,需要的话下次我贴出来。
mariadb [(none)]> use hellodb
database changed
mariadb [hellodb]> select * from students;
+-------+---------------+-----+--------+---------+-----------+
| stuid | name          | age | gender | classid | teacherid |
+-------+---------------+-----+--------+---------+-----------+
|     1 | shi zhongyu   |  22 | m      |       2 |         3 |
|     2 | shi potian    |  22 | m      |       1 |         7 |
|     3 | xie yanke     |  53 | m      |       2 |        16 |
|     4 | ding dian     |  32 | m      |       4 |         4 |
|     5 | yu yutong     |  26 | m      |       3 |         1 |
|     6 | shi qing      |  46 | m      |       5 |      null |
|     7 | xi ren        |  19 | f      |       3 |      null |
|     8 | lin daiyu     |  17 | f      |       7 |      null |
|     9 | ren yingying  |  20 | f      |       6 |      null |
|    10 | yue lingshan  |  19 | f      |       3 |      null |
|    11 | yuan chengzhi |  23 | m      |       6 |      null |
|    12 | wen qingqing  |  19 | f      |       1 |      null |
|    13 | tian boguang  |  33 | m      |       2 |      null |
|    14 | lu wushuang   |  17 | f      |       3 |      null |
|    15 | duan yu       |  19 | m      |       4 |      null |
|    16 | xu zhu        |  21 | m      |       1 |      null |
|    17 | lin chong     |  25 | m      |       4 |      null |
|    18 | hua rong      |  23 | m      |       7 |      null |
|    19 | xue baochai   |  18 | f      |       6 |      null |
|    20 | diao chan     |  19 | f      |       7 |      null |
|    21 | huang yueying |  22 | f      |       6 |      null |
|    22 | xiao qiao     |  20 | f      |       1 |      null |
|    23 | ma chao       |  23 | m      |       4 |      null |
|    24 | xu xian       |  27 | m      |    null |      null |
|    25 | sun dasheng   | 100 | m      |    null |      null |
+-------+---------------+-----+--------+---------+-----------+
25 rows in set (0.00 sec)

(创建表获取帮助命令)
mariadb [hellodb]> help create table;
name: 'create table'
description:
syntax:
create [temporary] table [if not exists] tbl_name
    (create_definition,...)
    [table_options]
    [partition_options]

or:

create [temporary] table [if not exists] tbl_name
    [(create_definition,...)]
    [table_options]
    [partition_options]
    select_statement

or:

create [temporary] table [if not exists] tbl_name
    { like old_tbl_name | (like old_tbl_name) }
  1. 克隆表
mariadb [hellodb]> create table newstudents select * from students;  (通过查询现存表创建;新表会被直接插入查询而来的数据)
query ok, 25 rows affected (0.01 sec)
records: 25  duplicates: 0  warnings: 0

mariadb [hellodb]> show tables;
+-------------------+
| tables_in_hellodb |
+-------------------+
| classes           |
| coc               |
| courses           |
| newstudents       |
| scores            |
| students          |
| teachers          |
| toc               |
+-------------------+
8 rows in set (0.00 sec)

mariadb [hellodb]> select * from newstudents;
+-------+---------------+-----+--------+---------+-----------+
| stuid | name          | age | gender | classid | teacherid |
+-------+---------------+-----+--------+---------+-----------+
|     1 | shi zhongyu   |  22 | m      |       2 |         3 |
|     2 | shi potian    |  22 | m      |       1 |         7 |
|     3 | xie yanke     |  53 | m      |       2 |        16 |
|     4 | ding dian     |  32 | m      |       4 |         4 |
|     5 | yu yutong     |  26 | m      |       3 |         1 |
|     6 | shi qing      |  46 | m      |       5 |      null |
|     7 | xi ren        |  19 | f      |       3 |      null |
|     8 | lin daiyu     |  17 | f      |       7 |      null |
|     9 | ren yingying  |  20 | f      |       6 |      null |
|    10 | yue lingshan  |  19 | f      |       3 |      null |
|    11 | yuan chengzhi |  23 | m      |       6 |      null |
|    12 | wen qingqing  |  19 | f      |       1 |      null |
|    13 | tian boguang  |  33 | m      |       2 |      null |
|    14 | lu wushuang   |  17 | f      |       3 |      null |
|    15 | duan yu       |  19 | m      |       4 |      null |
|    16 | xu zhu        |  21 | m      |       1 |      null |
|    17 | lin chong     |  25 | m      |       4 |      null |
|    18 | hua rong      |  23 | m      |       7 |      null |
|    19 | xue baochai   |  18 | f      |       6 |      null |
|    20 | diao chan     |  19 | f      |       7 |      null |
|    21 | huang yueying |  22 | f      |       6 |      null |
|    22 | xiao qiao     |  20 | f      |       1 |      null |
|    23 | ma chao       |  23 | m      |       4 |      null |
|    24 | xu xian       |  27 | m      |    null |      null |
|    25 | sun dasheng   | 100 | m      |    null |      null |
+-------+---------------+-----+--------+---------+-----------+
25 rows in set (0.00 sec)

(注意:这样不会把主键之类的复制过来,只是复制数据,表结构不一样)如下:
mariadb [hellodb]> desc newstudents;
+-----------+---------------------+------+-----+---------+-------+
| field     | type                | null | key | default | extra |
+-----------+---------------------+------+-----+---------+-------+
| stuid     | int(10) unsigned    | no   |     | 0       |       |
| name      | varchar(50)         | no   |     | null    |       |
| age       | tinyint(3) unsigned | no   |     | null    |       |
| gender    | enum('f','m')       | no   |     | null    |       |
| classid   | tinyint(3) unsigned | yes  |     | null    |       |
| teacherid | int(10) unsigned    | yes  |     | null    |       |
+-----------+---------------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

mariadb [hellodb]> desc students;
+-----------+---------------------+------+-----+---------+----------------+
| field     | type                | null | key | default | extra          |
+-----------+---------------------+------+-----+---------+----------------+
| stuid     | int(10) unsigned    | no   | pri | null    | auto_increment |
| name      | varchar(50)         | no   |     | null    |                |
| age       | tinyint(3) unsigned | no   |     | null    |                |
| gender    | enum('f','m')       | no   |     | null    |                |
| classid   | tinyint(3) unsigned | yes  |     | null    |                |
| teacherid | int(10) unsigned    | yes  |     | null    |                |
+-----------+---------------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)

通过复制现存的表的表结构创建,但不复制数据  
mariadb [hellodb]> create table newstudents2 like students;
query ok, 0 rows affected (0.01 sec)

mariadb [hellodb]> select * from newstudents2;   (这里查看数据是没有的)
empty set (0.00 sec)

mariadb [hellodb]> desc newstudents2;    (但是有表结构)
+-----------+---------------------+------+-----+---------+----------------+
| field     | type                | null | key | default | extra          |
+-----------+---------------------+------+-----+---------+----------------+
| stuid     | int(10) unsigned    | no   | pri | null    | auto_increment |
| name      | varchar(50)         | no   |     | null    |                |
| age       | tinyint(3) unsigned | no   |     | null    |                |
| gender    | enum('f','m')       | no   |     | null    |                |
| classid   | tinyint(3) unsigned | yes  |     | null    |                |
| teacherid | int(10) unsigned    | yes  |     | null    |                |
+-----------+---------------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)
  1. 表查看
查看支持的engine类型:
mariadb [hellodb]> show engines;

+--------------------+---------+----------------------------------------------------------------------------------+--------------+------+------------+
| engine             | support | comment                                                                          | transactions | xa   | savepoints |
+--------------------+---------+----------------------------------------------------------------------------------+--------------+------+------------+
| csv                | yes     | stores tables as csv files                                                       | no           | no   | no         |
| mrg_myisam         | yes     | collection of identical myisam tables                                            | no           | no   | no         |
| myisam             | yes     | non-transactional engine with good performance and small data footprint          | no           | no   | no         |
| sequence           | yes     | generated tables filled with sequential values                                   | yes          | no   | yes        |
| performance_schema | yes     | performance schema                                                               | no           | no   | no         |
| memory             | yes     | hash based, stored in memory, useful for temporary tables                        | no           | no   | no         |
| aria               | yes     | crash-safe tables with myisam heritage                                           | no           | no   | no         |
| innodb             | default | supports transactions, row-level locking, foreign keys and encryption for tables | yes          | yes  | yes        |
+--------------------+---------+----------------------------------------------------------------------------------+--------------+------+------------+
8 rows in set (0.00 sec)

查看表:
mariadb [hellodb]> show tables ;   (列出当前数据库中的所有表)
+-------------------+
| tables_in_hellodb |
+-------------------+
| classes           |
| coc               |
| courses           |
| newstudents       |
| newstudents2      |
| scores            |
| students          |
| teachers          |
| toc               |
+-------------------+
9 rows in set (0.00 sec)

mariadb [hellodb]> show tables from mysql;   (指明数据库查看这个数据库的表)
+---------------------------+
| tables_in_mysql           |
+---------------------------+
| column_stats              |
| columns_priv              |
| db                        |
| event                     |
| func                      |
| general_log               |
| gtid_slave_pos            |
| help_category             |
| help_keyword              |
| help_relation             |
| help_topic                |
| host                      |
| index_stats               |
| innodb_index_stats        |
| innodb_table_stats        |
| plugin                    |
| proc                      |
| procs_priv                |
| proxies_priv              |
| roles_mapping             |
| servers                   |
| slow_log                  |
| table_stats               |
| tables_priv               |
| time_zone                 |
| time_zone_leap_second     |
| time_zone_name            |
| time_zone_transition      |
| time_zone_transition_type |
| user                      |
+---------------------------+
30 rows in set (0.00 sec)

查看表结构:

mariadb [hellodb]> desc students;
+-----------+---------------------+------+-----+---------+----------------+
| field     | type                | null | key | default | extra          |
+-----------+---------------------+------+-----+---------+----------------+
| stuid     | int(10) unsigned    | no   | pri | null    | auto_increment |
| name      | varchar(50)         | no   |     | null    |                |
| age       | tinyint(3) unsigned | no   |     | null    |                |
| gender    | enum('f','m')       | no   |     | null    |                |
| classid   | tinyint(3) unsigned | yes  |     | null    |                |
| teacherid | int(10) unsigned    | yes  |     | null    |                |
+-----------+---------------------+------+-----+---------+----------------+

表结构字段的意思。
1. field:字段表示的是别名
2. type:字段表示的是列的数据类型
3. null :字段表示这个列是否能取空值
4. key :在mysql中key 和index 是一样的意思,这个key列可能会看到有如下的值:pri(主键)、mul(普通的b-tree索引)、uni(唯一索引)
5. default: 列的默认值
6. extra :其它信息

查看指定表的创建命令:  (既创建过程)
mariadb [hellodb]> show create table students;
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| table    | create table                                                                                                                                                                                                                                                                                                                                                    |
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| students | create table `students` (
  `stuid` int(10) unsigned not null auto_increment,
  `name` varchar(50) not null,
  `age` tinyint(3) unsigned not null,
  `gender` enum('f','m') not null,
  `classid` tinyint(3) unsigned default null,
  `teacherid` int(10) unsigned default null,
  primary key (`stuid`)
) engine=innodb auto_increment=26 default charset=utf8 |
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

查看看表的状态:(查看指定某个表状态要加单引号)
mariadb [hellodb]> show table status like 'students'\g; 
*************************** 1. row ***************************
           name: students
         engine: innodb
        version: 10
     row_format: dynamic
           rows: 25
 avg_row_length: 655
    data_length: 16384
max_data_length: 0
   index_length: 0
      data_free: 0
 auto_increment: 26
    create_time: 2019-11-20 21:19:51
    update_time: null
     check_time: null
      collation: utf8_general_ci
       checksum: null
 create_options: 
        comment: 
1 row in set (0.00 sec)

查看库中所有表的状态:
mariadb [hellodb]> show table status from hellodb\g;
*************************** 1. row ***************************
           name: classes
         engine: innodb
        version: 10
     row_format: dynamic
           rows: 8
 avg_row_length: 2048
    data_length: 16384
max_data_length: 0
   index_length: 0
      data_free: 0
 auto_increment: 9
    create_time: 2019-11-20 21:19:51
    update_time: null
     check_time: null
      collation: utf8_general_ci
       checksum: null
 create_options: 
        comment: 
*************************** 2. row ***************************
           name: coc
         engine: innodb
        version: 10
     row_format: dynamic
           rows: 14
 avg_row_length: 1170
    data_length: 16384
max_data_length: 0
   index_length: 0
      data_free: 0
 auto_increment: 15
    create_time: 2019-11-20 21:19:51
    update_time: null
     check_time: null
      collation: utf8_general_ci
       checksum: null
 create_options: 
        comment: 
.
.
.(省略证明我不是来混行数的)
.
.
*************************** 8. row ***************************
           name: teachers
         engine: innodb   (这里是使用什么存储引擎的意思)
        version: 10
     row_format: dynamic
           rows: 4
 avg_row_length: 4096
    data_length: 16384
max_data_length: 0
   index_length: 0
      data_free: 0
 auto_increment: 5
    create_time: 2019-11-20 21:19:51
    update_time: null
     check_time: null
      collation: utf8_general_ci
       checksum: null
 create_options: 
        comment: 
*************************** 9. row ***************************
           name: toc
         engine: innodb
        version: 10
     row_format: dynamic
           rows: 0
 avg_row_length: 0
    data_length: 16384
max_data_length: 0
   index_length: 0
      data_free: 0
 auto_increment: 1
    create_time: 2019-11-20 21:19:51
    update_time: null
     check_time: null
      collation: utf8_general_ci
       checksum: null
 create_options: 
        comment: 
9 rows in set (0.00 sec)
  1. 修改删除表
删除表:
mariadb [hellodb]> show tables;
+-------------------+
| tables_in_hellodb |
+-------------------+
| classes           |
| coc               |
| courses           |
| newstudents       |
| newstudents2      |
| scores            |
| students          |
| students2         |
| teachers          |
| toc               |
+-------------------+
10 rows in set (0.00 sec)

mariadb [hellodb]> drop table newstudents2;
query ok, 0 rows affected (0.00 sec)

mariadb [hellodb]> show tables;
+-------------------+
| tables_in_hellodb |
+-------------------+
| classes           |
| coc               |
| courses           |
| newstudents       |
| scores            |
| students          |
| students2         |
| teachers          |
| toc               |
+-------------------+
9 rows in set (0.00 sec)

查看修改表帮助:
mariadb [hellodb]> help alter table
name: 'alter table'
description:
syntax:
alter [online | offline] [ignore] table tbl_name
    [alter_specification [, alter_specification] ...]
    [partition_options]

修改表:
mariadb [hellodb]> show tables;
+-------------------+
| tables_in_hellodb |
+-------------------+
| classes           |
| coc               |
| courses           |
| scores            |
| students          |
| teachers          |
| toc               |
+-------------------+
7 rows in set (0.00 sec)

mariadb [hellodb]> alter table students rename s1;   (修改表名为s1)
query ok, 0 rows affected (0.00 sec)

mariadb [hellodb]> select * from students;
error 1146 (42s02): table 'hellodb.students' doesn't exist
mariadb [hellodb]> show tables;
+-------------------+
| tables_in_hellodb |
+-------------------+
| classes           |
| coc               |
| courses           |
| s1                |
| scores            |
| teachers          |
| toc               |
+-------------------+
7 rows in set (0.00 sec)

mariadb [hellodb]> alter table s1 add phone varchar(11) after name; (在name字段后面添加phone字段)  add:添加字段   varchar可变的 字符长度为11为
query ok, 0 rows affected (0.01 sec)
records: 0  duplicates: 0  warnings: 0

mariadb [hellodb]> select * from s1;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | shi zhongyu   | null  |  22 | m      |       2 |         3 |
|     2 | shi potian    | null  |  22 | m      |       1 |         7 |
|     3 | xie yanke     | null  |  53 | m      |       2 |        16 |
|     4 | ding dian     | null  |  32 | m      |       4 |         4 |
|     5 | yu yutong     | null  |  26 | m      |       3 |         1 |
|     6 | shi qing      | null  |  46 | m      |       5 |      null |
|     7 | xi ren        | null  |  19 | f      |       3 |      null |
|     8 | lin daiyu     | null  |  17 | f      |       7 |      null |
|     9 | ren yingying  | null  |  20 | f      |       6 |      null |
|    10 | yue lingshan  | null  |  19 | f      |       3 |      null |
|    11 | yuan chengzhi | null  |  23 | m      |       6 |      null |
|    12 | wen qingqing  | null  |  19 | f      |       1 |      null |
|    13 | tian boguang  | null  |  33 | m      |       2 |      null |
|    14 | lu wushuang   | null  |  17 | f      |       3 |      null |
|    15 | duan yu       | null  |  19 | m      |       4 |      null |
|    16 | xu zhu        | null  |  21 | m      |       1 |      null |
|    17 | lin chong     | null  |  25 | m      |       4 |      null |
|    18 | hua rong      | null  |  23 | m      |       7 |      null |
|    19 | xue baochai   | null  |  18 | f      |       6 |      null |
|    20 | diao chan     | null  |  19 | f      |       7 |      null |
|    21 | huang yueying | null  |  22 | f      |       6 |      null |
|    22 | xiao qiao     | null  |  20 | f      |       1 |      null |
|    23 | ma chao       | null  |  23 | m      |       4 |      null |
|    24 | xu xian       | null  |  27 | m      |    null |      null |
|    25 | sun dasheng   | null  | 100 | m      |    null |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
25 rows in set (0.00 sec)

mariadb [hellodb]> alter table s1 modify phone int;  (把phone的数据类型改为int)
query ok, 25 rows affected (0.01 sec)              
records: 25  duplicates: 0  warnings: 0

mariadb [hellodb]> desc s1
    -> ;
+-----------+---------------------+------+-----+---------+----------------+
| field     | type                | null | key | default | extra          |
+-----------+---------------------+------+-----+---------+----------------+
| stuid     | int(10) unsigned    | no   | pri | null    | auto_increment |
| name      | varchar(50)         | no   |     | null    |                |
| phone     | int(11)             | yes  |     | null    |                |
| age       | tinyint(3) unsigned | no   |     | null    |                |
| gender    | enum('f','m')       | no   |     | null    |                |
| classid   | tinyint(3) unsigned | yes  |     | null    |                |
| teacherid | int(10) unsigned    | yes  |     | null    |                |
+-----------+---------------------+------+-----+---------+----------------+
7 rows in set (0.00 sec)

(这些就不一一解释了有兴趣的可以自己试一试)
alter table s1 change column phone mobile char(11);
alter table s1 drop column mobile;
alter table s1 character set utf8;
alter table s1 change name name varchar(20) character set utf8;
alter table students add gender enum('m','f');
aletr table students change id sid int unsigned not null primary key;
alter table students drop primary key ;
alter table students drop primary key ;
desc students;
alter table students drop age;

dml语句

dml: insert, delete, update

insert 语句
功能:一次插入一行或多行数据 语法

update 语句
语句用于修改表中的数据。 注意:一定要有限制条件,否则将修改所有行的指定字段

delete语句
语句用于删除表中的行。 注意:一定要有限制条件,否则将清空表中的所有数据
可以在不删除表的情况下删除所有的行。这意味着表的结构、属性和索引都是完整的:
delete from table_name 或者 delete * from table_name
  1. insert语句实验: 三种语句
mariadb [hellodb]> help insert;
name: 'insert'
description:
syntax:
insert [low_priority | delayed | high_priority] [ignore]
    [into] tbl_name [(col_name,...)]
    {values | value} ({expr | default},...),(...),...
    [ on duplicate key update
      col_name=expr
        [, col_name=expr] ... ]

or:

insert [low_priority | delayed | high_priority] [ignore]
    [into] tbl_name
    set col_name={expr | default}, ...
    [ on duplicate key update
      col_name=expr
        [, col_name=expr] ... ]

or:

insert [low_priority | high_priority] [ignore]
    [into] tbl_name [(col_name,...)]
    select ...
    [ on duplicate key update
      col_name=expr
        [, col_name=expr] ... ]
  • 第一种语法
mariadb [hellodb]> insert into s1 values(26,'xietingfeng',null,23,'m',2,1); (添加一行表记录) 
query ok, 1 row affected (0.00 sec)

mariadb [hellodb]> select * from s1;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         3 |
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|     3 | xie yanke     |  null |  53 | m      |       2 |        16 |
|     4 | ding dian     |  null |  32 | m      |       4 |         4 |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|     6 | shi qing      |  null |  46 | m      |       5 |      null |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    13 | tian boguang  |  null |  33 | m      |       2 |      null |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|    15 | duan yu       |  null |  19 | m      |       4 |      null |
|    16 | xu zhu        |  null |  21 | m      |       1 |      null |
|    17 | lin chong     |  null |  25 | m      |       4 |      null |
|    18 | hua rong      |  null |  23 | m      |       7 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|    23 | ma chao       |  null |  23 | m      |       4 |      null |
|    24 | xu xian       |  null |  27 | m      |    null |      null |
|    25 | sun dasheng   |  null | 100 | m      |    null |      null |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
+-------+---------------+-------+-----+--------+---------+-----------+
26 rows in set (0.00 sec)

(如果出现这个提示可能是你少写了一个字段或者写错了)
mariadb [hellodb]> insert into s1 values(26,'xietingfeng',23,'m',2,1);
error 1136 (21s01): column count doesn't match value count at row 1

注意:如果想省略字段名的话,只能所有字段都赋值的话可以省略,单个赋值不可以省略。
如下:挑出三个字段来赋值,必须对应的写上。
mariadb [hellodb]> insert into s1(name,age,classid) values ('liudehua',18,1);
query ok, 1 row affected (0.00 sec)

mariadb [hellodb]> select * from s1;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         3 |
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|     3 | xie yanke     |  null |  53 | m      |       2 |        16 |
|     4 | ding dian     |  null |  32 | m      |       4 |         4 |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|     6 | shi qing      |  null |  46 | m      |       5 |      null |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    13 | tian boguang  |  null |  33 | m      |       2 |      null |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|    15 | duan yu       |  null |  19 | m      |       4 |      null |
|    16 | xu zhu        |  null |  21 | m      |       1 |      null |
|    17 | lin chong     |  null |  25 | m      |       4 |      null |
|    18 | hua rong      |  null |  23 | m      |       7 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|    23 | ma chao       |  null |  23 | m      |       4 |      null |
|    24 | xu xian       |  null |  27 | m      |    null |      null |
|    25 | sun dasheng   |  null | 100 | m      |    null |      null |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
27 rows in set (0.00 sec)              (↑ 这里是因为表结构设置默认不允许为空随机分配的值)

一次行两条记录赋值:
mariadb [hellodb]> insert into s1(name,age,gender,classid) values('mahuateng',20,'m',3),('wuyanzu',19,'m',4);
query ok, 2 rows affected (0.00 sec)
records: 2  duplicates: 0  warnings: 0

mariadb [hellodb]> select * from s1;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         3 |
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|     3 | xie yanke     |  null |  53 | m      |       2 |        16 |
|     4 | ding dian     |  null |  32 | m      |       4 |         4 |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|     6 | shi qing      |  null |  46 | m      |       5 |      null |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    13 | tian boguang  |  null |  33 | m      |       2 |      null |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|    15 | duan yu       |  null |  19 | m      |       4 |      null |
|    16 | xu zhu        |  null |  21 | m      |       1 |      null |
|    17 | lin chong     |  null |  25 | m      |       4 |      null |
|    18 | hua rong      |  null |  23 | m      |       7 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|    23 | ma chao       |  null |  23 | m      |       4 |      null |
|    24 | xu xian       |  null |  27 | m      |    null |      null |
|    25 | sun dasheng   |  null | 100 | m      |    null |      null |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|    28 | mahuateng     |  null |  20 | m      |       3 |      null |
|    29 | wuyanzu       |  null |  19 | m      |       4 |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
29 rows in set (0.00 sec)
  • 第二种语法
mariadb [hellodb]> insert s1 set name='wuzetian',age=21,gender='f';
query ok, 1 row affected (0.00 sec)

mariadb [hellodb]> select * from s1;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         3 |
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|     3 | xie yanke     |  null |  53 | m      |       2 |        16 |
|     4 | ding dian     |  null |  32 | m      |       4 |         4 |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|     6 | shi qing      |  null |  46 | m      |       5 |      null |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    13 | tian boguang  |  null |  33 | m      |       2 |      null |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|    15 | duan yu       |  null |  19 | m      |       4 |      null |
|    16 | xu zhu        |  null |  21 | m      |       1 |      null |
|    17 | lin chong     |  null |  25 | m      |       4 |      null |
|    18 | hua rong      |  null |  23 | m      |       7 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|    23 | ma chao       |  null |  23 | m      |       4 |      null |
|    24 | xu xian       |  null |  27 | m      |    null |      null |
|    25 | sun dasheng   |  null | 100 | m      |    null |      null |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|    28 | mahuateng     |  null |  20 | m      |       3 |      null |
|    29 | wuyanzu       |  null |  19 | m      |       4 |      null |
|    30 | wuzetian      |  null |  21 | f      |    null |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
30 rows in set (0.00 sec)
(使用的不多一般使用第一种了解一下)
  • 第三种语法
mariadb [hellodb]> select * from teachers;
+-----+---------------+-----+--------+
| tid | name          | age | gender |
+-----+---------------+-----+--------+
|   1 | song jiang    |  45 | m      |
|   2 | zhang sanfeng |  94 | m      |
|   3 | miejue shitai |  77 | f      |
|   4 | lin chaoying  |  93 | f      |
+-----+---------------+-----+--------+
4 rows in set (0.00 sec)

mariadb [hellodb]> insert s1 (name,classid,gender,age) select name,age,gender,18 from teachers;
query ok, 4 rows affected (0.00 sec)
records: 4  duplicates: 0  warnings: 0

mariadb [hellodb]> select * from s1;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         3 |
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|     3 | xie yanke     |  null |  53 | m      |       2 |        16 |
|     4 | ding dian     |  null |  32 | m      |       4 |         4 |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|     6 | shi qing      |  null |  46 | m      |       5 |      null |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    13 | tian boguang  |  null |  33 | m      |       2 |      null |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|    15 | duan yu       |  null |  19 | m      |       4 |      null |
|    16 | xu zhu        |  null |  21 | m      |       1 |      null |
|    17 | lin chong     |  null |  25 | m      |       4 |      null |
|    18 | hua rong      |  null |  23 | m      |       7 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|    23 | ma chao       |  null |  23 | m      |       4 |      null |
|    24 | xu xian       |  null |  27 | m      |    null |      null |
|    25 | sun dasheng   |  null | 100 | m      |    null |      null |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|    28 | mahuateng     |  null |  20 | m      |       3 |      null |
|    29 | wuyanzu       |  null |  19 | m      |       4 |      null |
|    30 | wuzetian      |  null |  21 | f      |    null |      null |
|    31 | song jiang    |  null |  18 | m      |      45 |      null |
|    32 | zhang sanfeng |  null |  18 | m      |      94 |      null |
|    33 | miejue shitai |  null |  18 | f      |      77 |      null |
|    34 | lin chaoying  |  null |  18 | f      |      93 |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
34 rows in set (0.00 sec)
(批量导入,a表参考b表的结构导入到b表中,主键必须是唯一的不可导入a表的主键)
  1. update语句
mariadb [hellodb]> help update;  (语句帮助)
name: 'update'
description:
syntax:
single-table syntax:

update [low_priority] [ignore] table_reference
    set col_name1={expr1|default} [, col_name2={expr2|default}] ...
    [where where_condition]
    [order by ...]
    [limit row_count]

mariadb [hellodb]> select * from n1;  (不加指定修改会把整个列都修改)
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         3 |
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|     3 | xie yanke     |  null |  53 | m      |       2 |        16 |
|     4 | ding dian     |  null |  32 | m      |       4 |         4 |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|     6 | shi qing      |  null |  46 | m      |       5 |      null |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    13 | tian boguang  |  null |  33 | m      |       2 |      null |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|    15 | duan yu       |  null |  19 | m      |       4 |      null |
|    16 | xu zhu        |  null |  21 | m      |       1 |      null |
|    17 | lin chong     |  null |  25 | m      |       4 |      null |
|    18 | hua rong      |  null |  23 | m      |       7 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|    23 | ma chao       |  null |  23 | m      |       4 |      null |
|    24 | xu xian       |  null |  27 | m      |    null |      null |
|    25 | sun dasheng   |  null | 100 | m      |    null |      null |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|    28 | mahuateng     |  null |  20 | m      |       3 |      null |
|    29 | wuyanzu       |  null |  19 | m      |       4 |      null |
|    30 | wuzetian      |  null |  21 | f      |    null |      null |
|    31 | song jiang    |  null |  18 | m      |      45 |      null |
|    32 | zhang sanfeng |  null |  18 | m      |      94 |      null |
|    33 | miejue shitai |  null |  18 | f      |      77 |      null |
|    34 | lin chaoying  |  null |  18 | f      |      93 |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
34 rows in set (0.00 sec)

mariadb [hellodb]> update n1 set teacherid=1; 
query ok, 32 rows affected (0.00 sec)
rows matched: 34  changed: 32  warnings: 0

mariadb [hellodb]> select * from n1;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         1 |
|     2 | shi potian    |  null |  22 | m      |       1 |         1 |
|     3 | xie yanke     |  null |  53 | m      |       2 |         1 |
|     4 | ding dian     |  null |  32 | m      |       4 |         1 |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|     6 | shi qing      |  null |  46 | m      |       5 |         1 |
|     7 | xi ren        |  null |  19 | f      |       3 |         1 |
|     8 | lin daiyu     |  null |  17 | f      |       7 |         1 |
|     9 | ren yingying  |  null |  20 | f      |       6 |         1 |
|    10 | yue lingshan  |  null |  19 | f      |       3 |         1 |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |         1 |
|    12 | wen qingqing  |  null |  19 | f      |       1 |         1 |
|    13 | tian boguang  |  null |  33 | m      |       2 |         1 |
|    14 | lu wushuang   |  null |  17 | f      |       3 |         1 |
|    15 | duan yu       |  null |  19 | m      |       4 |         1 |
|    16 | xu zhu        |  null |  21 | m      |       1 |         1 |
|    17 | lin chong     |  null |  25 | m      |       4 |         1 |
|    18 | hua rong      |  null |  23 | m      |       7 |         1 |
|    19 | xue baochai   |  null |  18 | f      |       6 |         1 |
|    20 | diao chan     |  null |  19 | f      |       7 |         1 |
|    21 | huang yueying |  null |  22 | f      |       6 |         1 |
|    22 | xiao qiao     |  null |  20 | f      |       1 |         1 |
|    23 | ma chao       |  null |  23 | m      |       4 |         1 |
|    24 | xu xian       |  null |  27 | m      |    null |         1 |
|    25 | sun dasheng   |  null | 100 | m      |    null |         1 |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|    27 | liudehua      |  null |  18 | f      |       1 |         1 |
|    28 | mahuateng     |  null |  20 | m      |       3 |         1 |
|    29 | wuyanzu       |  null |  19 | m      |       4 |         1 |
|    30 | wuzetian      |  null |  21 | f      |    null |         1 |
|    31 | song jiang    |  null |  18 | m      |      45 |         1 |
|    32 | zhang sanfeng |  null |  18 | m      |      94 |         1 |
|    33 | miejue shitai |  null |  18 | f      |      77 |         1 |
|    34 | lin chaoying  |  null |  18 | f      |      93 |         1 |
+-------+---------------+-------+-----+--------+---------+-----------+
34 rows in set (0.00 sec)

避免的方法:登陆的时候加-u进入安全模式,改模式下不加where指定不能更改。
[root@centos7 ~]#mysql -u -uroot -p123456
welcome to the mariadb monitor.  commands end with ; or \g.
your mariadb connection id is 11
server version: 10.2.29-mariadb-log mariadb server

copyright (c) 2000, 2018, oracle, mariadb corporation ab and others.

type 'help;' or '\h' for help. type '\c' to clear the current input statement.

mariadb [(none)]> update n1 set teacherid=2;
error 1046 (3d000): no database selected
mariadb [(none)]> 

或者修改配文件: 在mysql下面加上这一行
[root@centos7 ~]#vim /etc/my.cnf.d/mysql-clients.cnf
[mysql]
safe-updates

mariadb [hellodb]> update n1 set teacherid=2 where stuid=25;  (用where指定主键的某一范围修改)
query ok, 1 row affected (0.00 sec)
rows matched: 1  changed: 1  warnings: 0

mariadb [hellodb]> select * from n1
    -> ;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         1 |
|     2 | shi potian    |  null |  22 | m      |       1 |         1 |
|     3 | xie yanke     |  null |  53 | m      |       2 |         1 |
|     4 | ding dian     |  null |  32 | m      |       4 |         1 |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|     6 | shi qing      |  null |  46 | m      |       5 |         1 |
|     7 | xi ren        |  null |  19 | f      |       3 |         1 |
|     8 | lin daiyu     |  null |  17 | f      |       7 |         1 |
|     9 | ren yingying  |  null |  20 | f      |       6 |         1 |
|    10 | yue lingshan  |  null |  19 | f      |       3 |         1 |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |         1 |
|    12 | wen qingqing  |  null |  19 | f      |       1 |         1 |
|    13 | tian boguang  |  null |  33 | m      |       2 |         1 |
|    14 | lu wushuang   |  null |  17 | f      |       3 |         1 |
|    15 | duan yu       |  null |  19 | m      |       4 |         1 |
|    16 | xu zhu        |  null |  21 | m      |       1 |         1 |
|    17 | lin chong     |  null |  25 | m      |       4 |         1 |
|    18 | hua rong      |  null |  23 | m      |       7 |         1 |
|    19 | xue baochai   |  null |  18 | f      |       6 |         1 |
|    20 | diao chan     |  null |  19 | f      |       7 |         1 |
|    21 | huang yueying |  null |  22 | f      |       6 |         1 |
|    22 | xiao qiao     |  null |  20 | f      |       1 |         1 |
|    23 | ma chao       |  null |  23 | m      |       4 |         1 |
|    24 | xu xian       |  null |  27 | m      |    null |         1 |
|    25 | sun dasheng   |  null | 100 | m      |    null |         2 |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|    27 | liudehua      |  null |  18 | f      |       1 |         1 |
|    28 | mahuateng     |  null |  20 | m      |       3 |         1 |
|    29 | wuyanzu       |  null |  19 | m      |       4 |         1 |
|    30 | wuzetian      |  null |  21 | f      |    null |         1 |
|    31 | song jiang    |  null |  18 | m      |      45 |         1 |
|    32 | zhang sanfeng |  null |  18 | m      |      94 |         1 |
|    33 | miejue shitai |  null |  18 | f      |      77 |         1 |
|    34 | lin chaoying  |  null |  18 | f      |      93 |         1 |
+-------+---------------+-------+-----+--------+---------+-----------+
34 rows in set (0.00 sec)
注意:安全模式下,这样修改表必须有主键才可以修改。

添加主键方法:
mariadb [hellodb]> alter table n1 change stuid stuid int primary key;
  1. delete语句:(也要加where) (-u 和配置文件修改都支持)
mariadb [hellodb]> delete from n1 where stuid=28;  (删除这一行)
query ok, 1 row affected (0.00 sec)

mariadb [hellodb]> select * from n1; 
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+

|    24 | xu xian       |  null |  27 | m      |    null |         1 |
|    25 | sun dasheng   |  null | 100 | m      |    null |         2 |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|    27 | liudehua      |  null |  18 | f      |       1 |         1 |
|    29 | wuyanzu       |  null |  19 | m      |       4 |         1 |
|    30 | wuzetian      |  null |  21 | f      |    null |         1 |
|    31 | song jiang    |  null |  18 | m      |      45 |         1 |
|    32 | zhang sanfeng |  null |  18 | m      |      94 |         1 |
|    33 | miejue shitai |  null |  18 | f      |      77 |         1 |
|    34 | lin chaoying  |  null |  18 | f      |      93 |         1 |
+-------+---------------+-------+-----+--------+---------+-----------+
33 rows in set (0.00 sec)

(第二种清空数据保留表结构的方式)
mariadb [hellodb]> delete from n1;
query ok, 33 rows affected (0.00 sec)

mariadb [hellodb]> select * from n1;
empty set (0.00 sec)

mariadb [hellodb]> desc n1;  (表结构还在)
+-----------+---------------------+------+-----+---------+-------+
| field     | type                | null | key | default | extra |
+-----------+---------------------+------+-----+---------+-------+
| stuid     | int(11)             | no   | pri | null    |       |
| name      | varchar(50)         | no   |     | null    |       |
| phone     | int(11)             | yes  |     | null    |       |
| age       | tinyint(3) unsigned | no   |     | null    |       |
| gender    | enum('f','m')       | no   |     | null    |       |
| classid   | tinyint(3) unsigned | yes  |     | null    |       |
| teacherid | int(10) unsigned    | yes  |     | null    |       |
+-----------+---------------------+------+-----+---------+-------+
7 rows in set (0.00 sec)

dql语句

查询语句:select (单表和多表)

单表操作
语法:

select
[all | distinct | distinctrow ]
[sql_cache | sql_no_cache]
select_expr [, select_expr ...]
[from table_references
[where where_condition]
[group by {col_name | expr | position}
[asc | desc], ... [with rollup]]
[having where_condition]
[order by {col_name | expr | position}
[asc | desc], ...]
[limit {[offset,] row_count | row_count offset offset}]
[for update | lock in share mode]

说明:

  • 字段显示可以使用别名: col1 as alias1, col2 as alias2, ...
  • where子句:指明过滤条件以实现“选择”的功能: 过滤条件:布尔型表达式 算术操作符:+, -, *,
    /, % 比较操作符:=,<=>(相等或都为空), <>, !=(非标准sql), >, >=, <, <= between min_num
    and max_num in (element1, element2, ...) is null is not null select distinct 去除重复
    列,范例:select distinct gender from students; like: % 任意长度的任意字符 _ 任意单个字
    符 rlike:正则表达式,索引失效,不建议使用 regexp:匹配字符串可用正则表达式书写模式,
    同上 逻辑操作符:not,and,or,xor
  • group:根据指定的条件把查询结果进行“分组”以用于做“聚合”运算 常见聚合函数:avg(), max(),
    min(), count(), sum() having: 对分组聚合运算后的结果指定过滤条件
  • order by: 根据指定的字段对查询结果进行排序 升序:asc 降序:desc
  • limit [[offset,]row_count]:对查询的结果进行输出行数数量限制
  • 对查询结果中的数据请求施加“锁” for update: 写锁,独占或排它锁,只有一个读和写操作
    lock in share mode: 读锁,共享锁,同时多个读操作

范例:

truncate table tbl_name;
select
[all | distinct | distinctrow ]
[sql_cache | sql_no_cache]
select_expr [, select_expr ...]
[from table_references
[where where_condition]
[group by {col_name | expr | position}
[asc | desc], ... [with rollup]]
[having where_condition]
[order by {col_name | expr | position}
[asc | desc], ...]
[limit {[offset,] row_count | row_count offset offset}]
[for update | lock in share mode]
desc students;
insert into students values(1,'tom','m'),(2,'alice','f');
insert into students(id,name) values(3,'jack'),(4,'allen');
select * from students where id < 3;
select * from students where gender='m';
select * from students where gender is null;
select * from students where gender is not null;
select * from students order by name desc limit 2;
select * from students order by name desc limit 1,2;
select * from students where id >=2 and id <=4
select * from students where between 2 and 4
select * from students where name like ‘t%’
select * from students where name rlike '.*[lo].*';
select id stuid,name as stuname from students
  1. 单表实验:
  • 展示表里的所有内容*代表所有字段,也可以挑指定字段来显示。
mariadb [hellodb]> select * from s1;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         3 |
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|     3 | xie yanke     |  null |  53 | m      |       2 |        16 |
|     4 | ding dian     |  null |  32 | m      |       4 |         4 |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|     6 | shi qing      |  null |  46 | m      |       5 |      null |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
.... 省略掉
+-------+---------------+-------+-----+--------+---------+-----------+
34 rows in set (0.00 sec)
  • 甚至可以做数字运算
mariadb [hellodb]> select 2*3;
+-----+
| 2*3 |
+-----+
|   6 |
+-----+
1 row in set (0.01 sec)

mariadb [hellodb]> select 2*3 from teachers;  (指定一个表,表里有几行做几次数字运算和awk很相似)
+-----+
| 2*3 |
+-----+
|   6 |
|   6 |
|   6 |
|   6 |
+-----+
4 rows in set (0.00 sec)

mariadb [hellodb]> select * from teachers;
+-----+---------------+-----+--------+
| tid | name          | age | gender |
+-----+---------------+-----+--------+
|   1 | song jiang    |  45 | m      |
|   2 | zhang sanfeng |  94 | m      |
|   3 | miejue shitai |  77 | f      |
|   4 | lin chaoying  |  93 | f      |
+-----+---------------+-----+--------+
4 rows in set (0.00 sec)
  • 指定字段名更改 加*的话不行
mariadb [hellodb]> select '韦小宝',name from teachers;
+-----------+---------------+
| 韦小宝    | name          |
+-----------+---------------+
| 韦小宝    | song jiang    |
| 韦小宝    | zhang sanfeng |
| 韦小宝    | miejue shitai |
| 韦小宝    | lin chaoying  |
+-----------+---------------+
4 rows in set (0.00 sec)

mariadb [hellodb]> select '韦小宝',name,age,gender from teachers;
+-----------+---------------+-----+--------+
| 韦小宝    | name          | age | gender |
+-----------+---------------+-----+--------+
| 韦小宝    | song jiang    |  45 | m      |
| 韦小宝    | zhang sanfeng |  94 | m      |
| 韦小宝    | miejue shitai |  77 | f      |
| 韦小宝    | lin chaoying  |  93 | f      |
+-----------+---------------+-----+--------+
4 rows in set (0.00 sec)

(只是显示效果更改)
mariadb [hellodb]> select * from teachers;
+-----+---------------+-----+--------+
| tid | name          | age | gender |
+-----+---------------+-----+--------+
|   1 | song jiang    |  45 | m      |
|   2 | zhang sanfeng |  94 | m      |
|   3 | miejue shitai |  77 | f      |
|   4 | lin chaoying  |  93 | f      |
+-----+---------------+-----+--------+
4 rows in set (0.00 sec)
  • 对表头起别名显示
mariadb [hellodb]> select '韦小宝',name as "姓名",age "年龄",gender from teachers;
+-----------+---------------+--------+--------+
| 韦小宝    | 姓名          | 年龄   | gender |
+-----------+---------------+--------+--------+
| 韦小宝    | song jiang    |     45 | m      |
| 韦小宝    | zhang sanfeng |     94 | m      |
| 韦小宝    | miejue shitai |     77 | f      |
| 韦小宝    | lin chaoying  |     93 | f      |
+-----------+---------------+--------+--------+
4 rows in set (0.01 sec)
  • 行过滤:挑出性别不是m的 !=是非标准的sql语法 标准的为<>
mariadb [hellodb]>  select * from s1 where gender != 'm';  (只能在mysql数据库使用)
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|    30 | wuzetian      |  null |  21 | f      |    null |      null |
|    33 | miejue shitai |  null |  18 | f      |      77 |      null |
|    34 | lin chaoying  |  null |  18 | f      |      93 |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
14 rows in set (0.00 sec)

mariadb [hellodb]>  select * from s1 where gender <> 'm'; (所有sql数据库都可以使用)
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|    30 | wuzetian      |  null |  21 | f      |    null |      null |
|    33 | miejue shitai |  null |  18 | f      |      77 |      null |
|    34 | lin chaoying  |  null |  18 | f      |      93 |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
14 rows in set (0.00 sec)
  • 挑出大于30的
mariadb [hellodb]>  select * from s1 where age >=30;
+-------+--------------+-------+-----+--------+---------+-----------+
| stuid | name         | phone | age | gender | classid | teacherid |
+-------+--------------+-------+-----+--------+---------+-----------+
|     3 | xie yanke    |  null |  53 | m      |       2 |        16 |
|     4 | ding dian    |  null |  32 | m      |       4 |         4 |
|     6 | shi qing     |  null |  46 | m      |       5 |      null |
|    13 | tian boguang |  null |  33 | m      |       2 |      null |
|    25 | sun dasheng  |  null | 100 | m      |    null |      null |
+-------+--------------+-------+-----+--------+---------+-----------+
5 rows in set (0.00 sec)
  • 挑出20到30之间的
mariadb [hellodb]>  select * from s1 where age >=20 and age <=30;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         3 |
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |      null |
|    16 | xu zhu        |  null |  21 | m      |       1 |      null |
|    17 | lin chong     |  null |  25 | m      |       4 |      null |
|    18 | hua rong      |  null |  23 | m      |       7 |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|    23 | ma chao       |  null |  23 | m      |       4 |      null |
|    24 | xu xian       |  null |  27 | m      |    null |      null |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|    28 | mahuateng     |  null |  20 | m      |       3 |      null |
|    30 | wuzetian      |  null |  21 | f      |    null |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
15 rows in set (0.00 sec)

mariadb [hellodb]>  select * from s1 where age between 20 and 30; (结果等价于上面的)
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         3 |
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |      null |
|    16 | xu zhu        |  null |  21 | m      |       1 |      null |
|    17 | lin chong     |  null |  25 | m      |       4 |      null |
|    18 | hua rong      |  null |  23 | m      |       7 |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|    23 | ma chao       |  null |  23 | m      |       4 |      null |
|    24 | xu xian       |  null |  27 | m      |    null |      null |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|    28 | mahuateng     |  null |  20 | m      |       3 |      null |
|    30 | wuzetian      |  null |  21 | f      |    null |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
15 rows in set (0.00 sec)
  • 挑出大于30小于20的
mariadb [hellodb]>  select * from s1 where age >=30 or age <=20;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     3 | xie yanke     |  null |  53 | m      |       2 |        16 |
|     4 | ding dian     |  null |  32 | m      |       4 |         4 |
|     6 | shi qing      |  null |  46 | m      |       5 |      null |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    13 | tian boguang  |  null |  33 | m      |       2 |      null |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|    15 | duan yu       |  null |  19 | m      |       4 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|    25 | sun dasheng   |  null | 100 | m      |    null |      null |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|    28 | mahuateng     |  null |  20 | m      |       3 |      null |
|    29 | wuyanzu       |  null |  19 | m      |       4 |      null |
|    31 | song jiang    |  null |  18 | m      |      45 |      null |
|    32 | zhang sanfeng |  null |  18 | m      |      94 |      null |
|    33 | miejue shitai |  null |  18 | f      |      77 |      null |
|    34 | lin chaoying  |  null |  18 | f      |      93 |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
22 rows in set (0.00 sec)
  • 挑出1班,3班,6班的人
mariadb [hellodb]>  select * from s1 where classid in (1,3,6);
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|    16 | xu zhu        |  null |  21 | m      |       1 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|    28 | mahuateng     |  null |  20 | m      |       3 |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
14 rows in set (0.00 sec)
  • 查看班级id为空的
mariadb [hellodb]>  select * from s1 where classid is null;
+-------+-------------+-------+-----+--------+---------+-----------+
| stuid | name        | phone | age | gender | classid | teacherid |
+-------+-------------+-------+-----+--------+---------+-----------+
|    24 | xu xian     |  null |  27 | m      |    null |      null |
|    25 | sun dasheng |  null | 100 | m      |    null |      null |
|    30 | wuzetian    |  null |  21 | f      |    null |      null |
+-------+-------------+-------+-----+--------+---------+-----------+
3 rows in set (0.00 sec)
  • 查看班级id不为空的
mariadb [hellodb]>  select * from s1 where classid is not null;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         3 |
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|     3 | xie yanke     |  null |  53 | m      |       2 |        16 |
|     4 | ding dian     |  null |  32 | m      |       4 |         4 |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|     6 | shi qing      |  null |  46 | m      |       5 |      null |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    13 | tian boguang  |  null |  33 | m      |       2 |      null |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|    15 | duan yu       |  null |  19 | m      |       4 |      null |
|    16 | xu zhu        |  null |  21 | m      |       1 |      null |
|    17 | lin chong     |  null |  25 | m      |       4 |      null |
|    18 | hua rong      |  null |  23 | m      |       7 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|    23 | ma chao       |  null |  23 | m      |       4 |      null |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|    28 | mahuateng     |  null |  20 | m      |       3 |      null |
|    29 | wuyanzu       |  null |  19 | m      |       4 |      null |
|    31 | song jiang    |  null |  18 | m      |      45 |      null |
|    32 | zhang sanfeng |  null |  18 | m      |      94 |      null |
|    33 | miejue shitai |  null |  18 | f      |      77 |      null |
|    34 | lin chaoying  |  null |  18 | f      |      93 |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
31 rows in set (0.00 sec)
  • 添加空值必须指定为null
mariadb [hellodb]> insert students (name,age,gender,classid)values('abc',20,'m',null);
query ok, 1 row affected (0.00 sec)

mariadb [hellodb]>  select * from s1 where classid is null;
+-------+-------------+-------+-----+--------+---------+-----------+
| stuid | name        | phone | age | gender | classid | teacherid |
+-------+-------------+-------+-----+--------+---------+-----------+
|    24 | xu xian     |  null |  27 | m      |    null |      null |
|    25 | sun dasheng |  null | 100 | m      |    null |      null |
|    30 | wuzetian    |  null |  21 | f      |    null |      null |
|    38 | abc         |  null |  20 | m      |    null |      null |
+-------+-------------+-------+-----+--------+---------+-----------+
4 rows in set (0.00 sec)
  • 去除calssid重复的列
mariadb [hellodb]> select distinct classid from s1;
+---------+
| classid |
+---------+
|       2 |
|       1 |
|       4 |
|       3 |
|       5 |
|       7 |
|       6 |
|    null |
|      45 |
|      94 |
|      77 |
|      93 |
+---------+
12 rows in set (0.00 sec)
  • where语句模糊搜索匹配w开头的行 (like)
mariadb [hellodb]> select * from s1 where name like 'w%';
+-------+--------------+-------+-----+--------+---------+-----------+
| stuid | name         | phone | age | gender | classid | teacherid |
+-------+--------------+-------+-----+--------+---------+-----------+
|    12 | wen qingqing |  null |  19 | f      |       1 |      null |
|    29 | wuyanzu      |  null |  19 | m      |       4 |      null |
|    30 | wuzetian     |  null |  21 | f      |    null |      null |
+-------+--------------+-------+-----+--------+---------+-----------+
3 rows in set (0.00 sec)

mariadb [hellodb]> select * from s1 where name like '%w%'; (这个显示为包含w的行)
+-------+--------------+-------+-----+--------+---------+-----------+
| stuid | name         | phone | age | gender | classid | teacherid |
+-------+--------------+-------+-----+--------+---------+-----------+
|    12 | wen qingqing |  null |  19 | f      |       1 |      null |
|    14 | lu wushuang  |  null |  17 | f      |       3 |      null |
|    29 | wuyanzu      |  null |  19 | m      |       4 |      null |
|    30 | wuzetian     |  null |  21 | f      |    null |      null |
+-------+--------------+-------+-----+--------+---------+-----------+
4 rows in set (0.00 sec)
  • 查看字符串数量为三的:用三个下划线来表示
mariadb [hellodb]> select * from s1 where name like '___';
+-------+------+-------+-----+--------+---------+-----------+
| stuid | name | phone | age | gender | classid | teacherid |
+-------+------+-------+-----+--------+---------+-----------+
|    38 | abc  |  null |  20 | m      |    null |      null |
+-------+------+-------+-----+--------+---------+-----------+
1 row in set (0.00 sec)
  • rlike '^#'等价于like '#%'
mariadb [hellodb]> select * from s1 where name rlike '^x';
+-------+-------------+-------+-----+--------+---------+-----------+
| stuid | name        | phone | age | gender | classid | teacherid |
+-------+-------------+-------+-----+--------+---------+-----------+
|     3 | xie yanke   |  null |  53 | m      |       2 |        16 |
|     7 | xi ren      |  null |  19 | f      |       3 |      null |
|    16 | xu zhu      |  null |  21 | m      |       1 |      null |
|    19 | xue baochai |  null |  18 | f      |       6 |      null |
|    22 | xiao qiao   |  null |  20 | f      |       1 |      null |
|    24 | xu xian     |  null |  27 | m      |    null |      null |
|    26 | xietingfeng |  null |  23 | m      |       2 |         1 |
+-------+-------------+-------+-----+--------+---------+-----------+
7 rows in set (0.00 sec)

mariadb [hellodb]> select * from s1 where name like 'x%';
+-------+-------------+-------+-----+--------+---------+-----------+
| stuid | name        | phone | age | gender | classid | teacherid |
+-------+-------------+-------+-----+--------+---------+-----------+
|     3 | xie yanke   |  null |  53 | m      |       2 |        16 |
|     7 | xi ren      |  null |  19 | f      |       3 |      null |
|    16 | xu zhu      |  null |  21 | m      |       1 |      null |
|    19 | xue baochai |  null |  18 | f      |       6 |      null |
|    22 | xiao qiao   |  null |  20 | f      |       1 |      null |
|    24 | xu xian     |  null |  27 | m      |    null |      null |
|    26 | xietingfeng |  null |  23 | m      |       2 |         1 |
+-------+-------------+-------+-----+--------+---------+-----------+
7 rows in set (0.00 sec)
  • 建立一个表存储用户和密码
mariadb [hellodb]> create table user (id int primary key,name varchar(10) not null,password varchar(30) not null);
query ok, 0 rows affected (0.00 sec)

mariadb [hellodb]> insert user value(1,'alice','centos');
query ok, 1 row affected (0.00 sec)

mariadb [hellodb]> insert user value(2,'bob','linux');
query ok, 1 row affected (0.00 sec)

mariadb [hellodb]> select * from user;
+----+-------+----------+
| id | name  | password |
+----+-------+----------+
|  1 | alice | centos   |
|  2 | bob   | linux    |
+----+-------+----------+
2 rows in set (0.00 sec)
  • 使用sql注入(sql注入漏洞)
mariadb [hellodb]> select * from user where name='alice' and password='tuituibang'; (密码不对应返回空值)
empty set (0.00 sec)

mariadb [hellodb]> select * from user where name='alice'; -- ' and password='tuituibang'; (使用特殊符号密码不对应也可以查看)
+----+-------+----------+
| id | name  | password |
+----+-------+----------+
|  1 | alice | centos   |
+----+-------+----------+
1 row in set (0.00 sec)

构建一个复杂密码用户结果也一样

mariadb [hellodb]> insert user values(3,'admin','p@ssw)rd!');
query ok, 1 row affected (0.00 sec)

mariadb [hellodb]> select * from user;
+----+-------+-----------+
| id | name  | password  |
+----+-------+-----------+
|  1 | alice | centos    |
|  2 | bob   | linux     |
|  3 | admin | p@ssw)rd! |
+----+-------+-----------+
3 rows in set (0.00 sec)

mariadb [hellodb]> select * from user where name='admin'; -- ' and password='tuituibang';  (这里的引号数量是单数)
+----+-------+-----------+
| id | name  | password  |
+----+-------+-----------+
|  3 | admin | p@ssw)rd! |
+----+-------+-----------+
1 row in set (0.00 sec)

在登陆的时候构建一个奇怪的密码也可以登录 (注意这里的引号数量必须是成对的)
mariadb [hellodb]> select * from user where name='admin' and password=''  or '1=1';
+----+-------+-----------+
| id | name  | password  |
+----+-------+-----------+
|  1 | alice | centos    |
|  2 | bob   | linux     |
|  3 | admin | p@ssw)rd! |
+----+-------+-----------+
3 rows in set, 5 warnings (0.00 sec)

mariadb [hellodb]> select * from user where name='admin' and password=''  or '1'='1'; 
+----+-------+-----------+
| id | name  | password  |
+----+-------+-----------+
|  1 | alice | centos    |
|  2 | bob   | linux     |
|  3 | admin | p@ssw)rd! |
+----+-------+-----------+
3 rows in set (0.00 sec)

单表操作的分组统计

  • sql的聚合函数
avg(column)             返回某列的平均值
binary_checksum  
checksum     
checksum_agg     
count(column)           返回某列的行数(不包括null值)
count(*)                返回被选行数(函数返回在给定的选择中被选的行数)
count(distinct column)  返回相异结果的数目
first(column)           返回在指定的域中第一个记录的值(sqlserver2000 不支持)
last(column)            返回在指定的域中最后一个记录的值(sqlserver2000 不支持)
max(column)             返回某列的最高值
min(column)             返回某列的最低值
stdev(column)    
stdevp(column)   
sum(column)             返回某列的总和
var(column)  
varp(column)     
  • count 统计列的行数
mariadb [hellodb]> select count(stuid) from s1;
+--------------+
| count(stuid) |
+--------------+
|           35 |
+--------------+
1 row in set (0.00 sec)

mariadb [hellodb]> select count(classid) from s1;
+----------------+
| count(classid) |
+----------------+
|             31 |        (有空值不统计)
+----------------+
1 row in set (0.00 sec)


mariadb [hellodb]> select count(1) from s1; (跟count(主键)一样,只扫描主键)
+----------+
| count(1) |
+----------+
|       35 |
+----------+
1 row in set (0.00 sec)

mariadb [hellodb]> select count(*) from s1; (和count(主键)使用方式一样,但是在性能上有略微的区别,mysql对前者做了优化。)
+----------+
| count(*) |
+----------+
|       35 |
+----------+
1 row in set (0.00 sec)
  • 使用group by (根据指定的条件把查询结果进行“分组”以用于做“聚合”运算 常见聚合函数)统计男生女生分别多少个
mariadb [hellodb]> select gender,count(*) from s1 group by gender ;
+--------+----------+
| gender | count(*) |
+--------+----------+
| f      |       14 |
| m      |       21 |
+--------+----------+
2 rows in set (0.00 sec)

(起个别名)
mariadb [hellodb]> select gender 性别,count(*) 人数 from s1 group by gender ;
+--------+--------+
| 性别   | 人数   |
+--------+--------+
| f      |     14 |
| m      |     21 |
+--------+--------+
2 rows in set (0.00 sec)
  • avg 统计平均年龄
mariadb [hellodb]> select gender,avg(age) from s1 group by gender;
+--------+----------+
| gender | avg(age) |
+--------+----------+
| f      |  18.9286 |
| m      |  29.1905 |
+--------+----------+
2 rows in set (0.00 sec)
  • max 统计男女生最大的年龄
mariadb [hellodb]> select gender,avg(age),max(age) from s1 group by gender;
+--------+----------+----------+
| gender | avg(age) | max(age) |
+--------+----------+----------+
| f      |  18.9286 |       22 |
| m      |  29.1905 |      100 |
+--------+----------+----------+
2 rows in set (0.00 sec)
  • 分组之后过滤行的话不能加where 要加having (在group by后面使用)
mariadb [hellodb]> select classid,gender,avg(age) from s1 group by classid,gender;
+---------+--------+----------+              (过滤掉空的行)
| classid | gender | avg(age) |
+---------+--------+----------+
|    null | f      |  21.0000 |
|    null | m      |  49.0000 |
|       1 | f      |  19.0000 |
|       1 | m      |  21.5000 |
|       2 | m      |  32.7500 |
|       3 | f      |  18.3333 |
|       3 | m      |  23.0000 |
|       4 | m      |  23.6000 |
|       5 | m      |  46.0000 |
|       6 | f      |  20.0000 |
|       6 | m      |  23.0000 |
|       7 | f      |  18.0000 |
|       7 | m      |  23.0000 |
|      45 | m      |  18.0000 |
|      77 | f      |  18.0000 |
|      93 | f      |  18.0000 |
|      94 | m      |  18.0000 |
+---------+--------+----------+
17 rows in set (0.00 sec)

mariadb [hellodb]> select classid,gender,avg(age) from s1 group by classid,gender where classid is not null;
error 1064 (42000): you have an error in your sql syntax; check the manual that corresponds to your mariadb server version for the right syntax to use near 'where classid is not null' at line 1
mariadb [hellodb]> select classid,gender,avg(age) from s1 group by classid,gender having classid is not null;  (having: 对分组聚合运算后的结果指定过滤条件)
+---------+--------+----------+
| classid | gender | avg(age) |
+---------+--------+----------+
|       1 | f      |  19.0000 |
|       1 | m      |  21.5000 |
|       2 | m      |  32.7500 |
|       3 | f      |  18.3333 |
|       3 | m      |  23.0000 |
|       4 | m      |  23.6000 |
|       5 | m      |  46.0000 |
|       6 | f      |  20.0000 |
|       6 | m      |  23.0000 |
|       7 | f      |  18.0000 |
|       7 | m      |  23.0000 |
|      45 | m      |  18.0000 |
|      77 | f      |  18.0000 |
|      93 | f      |  18.0000 |
|      94 | m      |  18.0000 |
+---------+--------+----------+
15 rows in set (0.00 sec)
  • 分组前可以使用where过滤 (在group by之前添加)
mariadb [hellodb]> select classid,gender,avg(age) from s1 where classid is not null group by classid,gender;
+---------+--------+----------+
| classid | gender | avg(age) |
+---------+--------+----------+
|       1 | f      |  19.0000 |
|       1 | m      |  21.5000 |
|       2 | m      |  32.7500 |
|       3 | f      |  18.3333 |
|       3 | m      |  23.0000 |
|       4 | m      |  23.6000 |
|       5 | m      |  46.0000 |
|       6 | f      |  20.0000 |
|       6 | m      |  23.0000 |
|       7 | f      |  18.0000 |
|       7 | m      |  23.0000 |
|      45 | m      |  18.0000 |
|      77 | f      |  18.0000 |
|      93 | f      |  18.0000 |
|      94 | m      |  18.0000 |
+---------+--------+----------+
15 rows in set (0.00 sec)
  • order by 排序 单字段排序:默认按照字母正序排序
mariadb [hellodb]> select * from s1 order by name;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|    38 | abc           |  null |  20 | m      |    null |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|     4 | ding dian     |  null |  32 | m      |       4 |         4 |
|    15 | duan yu       |  null |  19 | m      |       4 |      null |
|    18 | hua rong      |  null |  23 | m      |       7 |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
|    34 | lin chaoying  |  null |  18 | f      |      93 |      null |
|    17 | lin chong     |  null |  25 | m      |       4 |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|    23 | ma chao       |  null |  23 | m      |       4 |      null |
|    28 | mahuateng     |  null |  20 | m      |       3 |      null |
|    33 | miejue shitai |  null |  18 | f      |      77 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|     6 | shi qing      |  null |  46 | m      |       5 |      null |
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         3 |
|    31 | song jiang    |  null |  18 | m      |      45 |      null |
|    25 | sun dasheng   |  null | 100 | m      |    null |      null |
|    13 | tian boguang  |  null |  33 | m      |       2 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    29 | wuyanzu       |  null |  19 | m      |       4 |      null |
|    30 | wuzetian      |  null |  21 | f      |    null |      null |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|     3 | xie yanke     |  null |  53 | m      |       2 |        16 |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|    24 | xu xian       |  null |  27 | m      |    null |      null |
|    16 | xu zhu        |  null |  21 | m      |       1 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|    32 | zhang sanfeng |  null |  18 | m      |      94 |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
35 rows in set (0.00 sec)
  • 倒序排序
mariadb [hellodb]> select * from s1 order by name desc;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|    32 | zhang sanfeng |  null |  18 | m      |      94 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |      null |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|    16 | xu zhu        |  null |  21 | m      |       1 |      null |
|    24 | xu xian       |  null |  27 | m      |    null |      null |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|     3 | xie yanke     |  null |  53 | m      |       2 |        16 |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|    30 | wuzetian      |  null |  21 | f      |    null |      null |
|    29 | wuyanzu       |  null |  19 | m      |       4 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    13 | tian boguang  |  null |  33 | m      |       2 |      null |
|    25 | sun dasheng   |  null | 100 | m      |    null |      null |
|    31 | song jiang    |  null |  18 | m      |      45 |      null |
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         3 |
|     6 | shi qing      |  null |  46 | m      |       5 |      null |
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    33 | miejue shitai |  null |  18 | f      |      77 |      null |
|    28 | mahuateng     |  null |  20 | m      |       3 |      null |
|    23 | ma chao       |  null |  23 | m      |       4 |      null |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|    17 | lin chong     |  null |  25 | m      |       4 |      null |
|    34 | lin chaoying  |  null |  18 | f      |      93 |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
|    18 | hua rong      |  null |  23 | m      |       7 |      null |
|    15 | duan yu       |  null |  19 | m      |       4 |      null |
|     4 | ding dian     |  null |  32 | m      |       4 |         4 |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|    38 | abc           |  null |  20 | m      |    null |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
35 rows in set (0.00 sec)
  • 指定asc排序 (asc:以数字大小从小到大排序,空值默认为0排在最前面)
mariadb [hellodb]> select * from s1 order by classid asc;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|    38 | abc           |  null |  20 | m      |    null |      null |
|    24 | xu xian       |  null |  27 | m      |    null |      null |
|    25 | sun dasheng   |  null | 100 | m      |    null |      null |
|    30 | wuzetian      |  null |  21 | f      |    null |      null |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|    16 | xu zhu        |  null |  21 | m      |       1 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         3 |
|    13 | tian boguang  |  null |  33 | m      |       2 |      null |
|     3 | xie yanke     |  null |  53 | m      |       2 |        16 |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|    28 | mahuateng     |  null |  20 | m      |       3 |      null |
|    23 | ma chao       |  null |  23 | m      |       4 |      null |
|     4 | ding dian     |  null |  32 | m      |       4 |         4 |
|    29 | wuyanzu       |  null |  19 | m      |       4 |      null |
|    17 | lin chong     |  null |  25 | m      |       4 |      null |
|    15 | duan yu       |  null |  19 | m      |       4 |      null |
|     6 | shi qing      |  null |  46 | m      |       5 |      null |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|    18 | hua rong      |  null |  23 | m      |       7 |      null |
|    31 | song jiang    |  null |  18 | m      |      45 |      null |
|    33 | miejue shitai |  null |  18 | f      |      77 |      null |
|    34 | lin chaoying  |  null |  18 | f      |      93 |      null |
|    32 | zhang sanfeng |  null |  18 | m      |      94 |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
35 rows in set (0.00 sec)
  • 还是按照数字从小到大排序但是空值排在最后面
mariadb [hellodb]> select * from s1 order by -classid desc;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|    16 | xu zhu        |  null |  21 | m      |       1 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         3 |
|    13 | tian boguang  |  null |  33 | m      |       2 |      null |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|     3 | xie yanke     |  null |  53 | m      |       2 |        16 |
|    28 | mahuateng     |  null |  20 | m      |       3 |      null |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|    29 | wuyanzu       |  null |  19 | m      |       4 |      null |
|    15 | duan yu       |  null |  19 | m      |       4 |      null |
|    23 | ma chao       |  null |  23 | m      |       4 |      null |
|    17 | lin chong     |  null |  25 | m      |       4 |      null |
|     4 | ding dian     |  null |  32 | m      |       4 |         4 |
|     6 | shi qing      |  null |  46 | m      |       5 |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|    18 | hua rong      |  null |  23 | m      |       7 |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|    31 | song jiang    |  null |  18 | m      |      45 |      null |
|    33 | miejue shitai |  null |  18 | f      |      77 |      null |
|    34 | lin chaoying  |  null |  18 | f      |      93 |      null |
|    32 | zhang sanfeng |  null |  18 | m      |      94 |      null |
|    25 | sun dasheng   |  null | 100 | m      |    null |      null |
|    30 | wuzetian      |  null |  21 | f      |    null |      null |
|    24 | xu xian       |  null |  27 | m      |    null |      null |
|    38 | abc           |  null |  20 | m      |    null |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
35 rows in set (0.00 sec)
  • 多字段排序 (先对性别排序在对年龄排序)
mariadb [hellodb]> select * from s1 order by gender , age;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|    33 | miejue shitai |  null |  18 | f      |      77 |      null |
|    34 | lin chaoying  |  null |  18 | f      |      93 |      null |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    30 | wuzetian      |  null |  21 | f      |    null |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
|    31 | song jiang    |  null |  18 | m      |      45 |      null |
|    32 | zhang sanfeng |  null |  18 | m      |      94 |      null |
|    15 | duan yu       |  null |  19 | m      |       4 |      null |
|    29 | wuyanzu       |  null |  19 | m      |       4 |      null |
|    28 | mahuateng     |  null |  20 | m      |       3 |      null |
|    38 | abc           |  null |  20 | m      |    null |      null |
|    16 | xu zhu        |  null |  21 | m      |       1 |      null |
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         3 |
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |      null |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|    18 | hua rong      |  null |  23 | m      |       7 |      null |
|    23 | ma chao       |  null |  23 | m      |       4 |      null |
|    17 | lin chong     |  null |  25 | m      |       4 |      null |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|    24 | xu xian       |  null |  27 | m      |    null |      null |
|     4 | ding dian     |  null |  32 | m      |       4 |         4 |
|    13 | tian boguang  |  null |  33 | m      |       2 |      null |
|     6 | shi qing      |  null |  46 | m      |       5 |      null |
|     3 | xie yanke     |  null |  53 | m      |       2 |        16 |
|    25 | sun dasheng   |  null | 100 | m      |    null |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
35 rows in set (0.00 sec)
  • 先对性别降序排序在对年龄正序排序。
mariadb [hellodb]> select * from s1 order by gender desc,age asc;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|    32 | zhang sanfeng |  null |  18 | m      |      94 |      null |
|    31 | song jiang    |  null |  18 | m      |      45 |      null |
|    29 | wuyanzu       |  null |  19 | m      |       4 |      null |
|    15 | duan yu       |  null |  19 | m      |       4 |      null |
|    38 | abc           |  null |  20 | m      |    null |      null |
|    28 | mahuateng     |  null |  20 | m      |       3 |      null |
|    16 | xu zhu        |  null |  21 | m      |       1 |      null |
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         3 |
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|    18 | hua rong      |  null |  23 | m      |       7 |      null |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|    23 | ma chao       |  null |  23 | m      |       4 |      null |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |      null |
|    17 | lin chong     |  null |  25 | m      |       4 |      null |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|    24 | xu xian       |  null |  27 | m      |    null |      null |
|     4 | ding dian     |  null |  32 | m      |       4 |         4 |
|    13 | tian boguang  |  null |  33 | m      |       2 |      null |
|     6 | shi qing      |  null |  46 | m      |       5 |      null |
|     3 | xie yanke     |  null |  53 | m      |       2 |        16 |
|    25 | sun dasheng   |  null | 100 | m      |    null |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|    34 | lin chaoying  |  null |  18 | f      |      93 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|    33 | miejue shitai |  null |  18 | f      |      77 |      null |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    30 | wuzetian      |  null |  21 | f      |    null |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
35 rows in set (0.00 sec)
  • 多字段排序之后无法在做过滤 (但是排序前可以)
mariadb [hellodb]> select * from s1 order by gender desc,age asc where classid is not null;
error 1064 (42000): you have an error in your sql syntax; check the manual that corresponds to your mariadb server version for the right syntax to use near 'where classid is not null' at line 1
mariadb [hellodb]> select * from s1 order by gender desc,age asc having classid is not null;
error 1064 (42000): you have an error in your sql syntax; check the manual that corresponds to your mariadb server version for the right syntax to use near 'having classid is not null' at line 1
mariadb [hellodb]> select * from s1 order by gender desc,age asc on classid is not null;
error 1064 (42000): you have an error in your sql syntax; check the manual that corresponds to your mariadb server version for the right syntax to use near 'on classid is not null' at line 1

(先过滤在排序)
mariadb [hellodb]> select * from s1 where classid is not null order by gender desc,age asc;  (和group by 一样还是在前面加)
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|    32 | zhang sanfeng |  null |  18 | m      |      94 |      null |
|    31 | song jiang    |  null |  18 | m      |      45 |      null |
|    29 | wuyanzu       |  null |  19 | m      |       4 |      null |
|    15 | duan yu       |  null |  19 | m      |       4 |      null |
|    28 | mahuateng     |  null |  20 | m      |       3 |      null |
|    16 | xu zhu        |  null |  21 | m      |       1 |      null |
|     1 | shi zhongyu   |  null |  22 | m      |       2 |         3 |
|     2 | shi potian    |  null |  22 | m      |       1 |         7 |
|    23 | ma chao       |  null |  23 | m      |       4 |      null |
|    26 | xietingfeng   |  null |  23 | m      |       2 |         1 |
|    11 | yuan chengzhi |  null |  23 | m      |       6 |      null |
|    18 | hua rong      |  null |  23 | m      |       7 |      null |
|    17 | lin chong     |  null |  25 | m      |       4 |      null |
|     5 | yu yutong     |  null |  26 | m      |       3 |         1 |
|     4 | ding dian     |  null |  32 | m      |       4 |         4 |
|    13 | tian boguang  |  null |  33 | m      |       2 |      null |
|     6 | shi qing      |  null |  46 | m      |       5 |      null |
|     3 | xie yanke     |  null |  53 | m      |       2 |        16 |
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|    33 | miejue shitai |  null |  18 | f      |      77 |      null |
|    34 | lin chaoying  |  null |  18 | f      |      93 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    10 | yue lingshan  |  null |  19 | f      |       3 |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|    22 | xiao qiao     |  null |  20 | f      |       1 |      null |
|     9 | ren yingying  |  null |  20 | f      |       6 |      null |
|    21 | huang yueying |  null |  22 | f      |       6 |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
31 rows in set (0.00 sec)
  • 后面的分组字段对调位置的话显示效果不一样但是数据还是一样的。(排序逻辑不一样)
mariadb [hellodb]> select gender,classid,avg(age) from s1 where classid is not null group by gender,classid;
+--------+---------+----------+
| gender | classid | avg(age) |
+--------+---------+----------+
| f      |       1 |  19.0000 |
| f      |       3 |  18.3333 |
| f      |       6 |  20.0000 |
| f      |       7 |  18.0000 |
| f      |      77 |  18.0000 |
| f      |      93 |  18.0000 |
| m      |       1 |  21.5000 |
| m      |       2 |  32.7500 |
| m      |       3 |  23.0000 |
| m      |       4 |  23.6000 |
| m      |       5 |  46.0000 |
| m      |       6 |  23.0000 |
| m      |       7 |  23.0000 |
| m      |      45 |  18.0000 |
| m      |      94 |  18.0000 |
+--------+---------+----------+
15 rows in set (0.00 sec)

mariadb [hellodb]> select gender,classid,avg(age) from s1 where classid is not null group by classid,gender;
+--------+---------+----------+
| gender | classid | avg(age) |
+--------+---------+----------+
| f      |       1 |  19.0000 |
| m      |       1 |  21.5000 |
| m      |       2 |  32.7500 |
| f      |       3 |  18.3333 |
| m      |       3 |  23.0000 |
| m      |       4 |  23.6000 |
| m      |       5 |  46.0000 |
| f      |       6 |  20.0000 |
| m      |       6 |  23.0000 |
| f      |       7 |  18.0000 |
| m      |       7 |  23.0000 |
| m      |      45 |  18.0000 |
| f      |      77 |  18.0000 |
| f      |      93 |  18.0000 |
| m      |      94 |  18.0000 |
+--------+---------+----------+
15 rows in set (0.00 sec)
  • limit [[offset,]row_count]:对查询的结果进行输出行数数量限制
    正序排序取岁数最小的前10名 limit 作为限制条件
mariadb [hellodb]> select * from s1 order by age limit 10;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|    14 | lu wushuang   |  null |  17 | f      |       3 |      null |
|     8 | lin daiyu     |  null |  17 | f      |       7 |      null |
|    32 | zhang sanfeng |  null |  18 | m      |      94 |      null |
|    34 | lin chaoying  |  null |  18 | f      |      93 |      null |
|    31 | song jiang    |  null |  18 | m      |      45 |      null |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|    33 | miejue shitai |  null |  18 | f      |      77 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
10 rows in set (0.00 sec)
  • 跳过前三行取岁数最小的前10名
mariadb [hellodb]> select * from s1 order by age limit 3,10;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | name          | phone | age | gender | classid | teacherid |
+-------+---------------+-------+-----+--------+---------+-----------+
|    33 | miejue shitai |  null |  18 | f      |      77 |      null |
|    19 | xue baochai   |  null |  18 | f      |       6 |      null |
|    31 | song jiang    |  null |  18 | m      |      45 |      null |
|    27 | liudehua      |  null |  18 | f      |       1 |      null |
|    34 | lin chaoying  |  null |  18 | f      |      93 |      null |
|    20 | diao chan     |  null |  19 | f      |       7 |      null |
|    12 | wen qingqing  |  null |  19 | f      |       1 |      null |
|    15 | duan yu       |  null |  19 | m      |       4 |      null |
|     7 | xi ren        |  null |  19 | f      |       3 |      null |
|    29 | wuyanzu       |  null |  19 | m      |       4 |      null |
+-------+---------------+-------+-----+--------+---------+-----------+
10 rows in set (0.00 sec)
  • 去重之后在做过滤 (这样取出来的数值比较准确)
mariadb [hellodb]> select distinct age from s1 order by age limit 3; (去重取前三个)
+-----+
| age |
+-----+
|  17 |
|  18 |
|  19 |
+-----+
3 rows in set (0.00 sec)

mariadb [hellodb]> select distinct age from s1 order by age limit 3,6; (去重跳过前3行取6行)
+-----+
| age |
+-----+
|  20 |
|  21 |
|  22 |
|  23 |
|  25 |
|  26 |
+-----+
6 rows in set (0.00 sec)