MYSQL 表的全面总结

1、创建表

1.1、创建表基本语法

create table tablename (column_name_1 column_type_1 constraints，
column_name_2 column_type_2 constraints ， ……）

column_name 是列的名字
column_type 是列的数据类型
contraints 是这个列的约束条件

1.1.1、创建一张简单的表

mysql> create table orders (ordername varchar(10),createtime date,ordermoney decimal(10,2),ordernumber int(2));
query ok, 0 rows affected (0.23 sec)

1.1.2、查看创建表定义

结构化定义：

mysql> desc orders;
+-------------+---------------+------+-----+---------+-------+
| field       | type          | null | key | default | extra |
+-------------+---------------+------+-----+---------+-------+
| ordername   | varchar(10)   | yes  |     | null    |       |
| createtime  | date          | yes  |     | null    |       |
| ordermoney  | decimal(10,2) | yes  |     | null    |       |
| ordernumber | int(2)        | yes  |     | null    |       |
+-------------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

表详细定义：

查看详细的表定义：

mysql> show create table orders \g;
*************************** 1. row ***************************
       table: orders
create table: create table `orders` (
  `ordername` varchar(10) default null,
  `createtime` date default null,
  `ordermoney` decimal(10,2) default null,
  `ordernumber` int(2) default null
) engine=innodb default charset=latin1
1 row in set (0.00 sec)

error:
no query specified

由此可以看到表的  engine（存储引擎）是innodb

　　　　　　　　 charset（字符集）是latin1

“\g”选项的含义是使得记录能够按照字段竖着排列，对于内容比较长的记录更易于显示。

2、删除表

命令：

drop table tablename

删除orders：

mysql> drop table orders
    -> ;
query ok, 0 rows affected (0.14 sec)

3、修改表

3.1、修改表类型命令

alter table tablename modify [column] column_definition [first | after col_name]

例：修改表 orders 的 name 字段定义，将 varchar(10)改为 varchar(20) ：

mysql> alter table orders modify ordername varchar(20);
query ok, 0 rows affected (0.11 sec)
records: 0  duplicates: 0  warnings: 0

mysql> desc orders;
+-------------+---------------+------+-----+---------+-------+
| field       | type          | null | key | default | extra |
+-------------+---------------+------+-----+---------+-------+
| ordername   | varchar(20)   | yes  |     | null    |       |
| createtime  | date          | yes  |     | null    |       |
| ordermoney  | decimal(10,2) | yes  |     | null    |       |
| ordernumber | int(2)        | yes  |     | null    |       |
+-------------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

3.2、字段改名命令

alter table tablename change [column] old_col_name column_definition
[first|after col_name]

例：表 orders 上将ordernumber修改为ordernumbers

mysql> alter table orders change column ordernumber ordernumbers int(4);
query ok, 0 rows affected (0.06 sec)
records: 0  duplicates: 0  warnings: 0

mysql> desc orders;
+--------------+---------------+------+-----+---------+-------+
| field        | type          | null | key | default | extra |
+--------------+---------------+------+-----+---------+-------+
| ordername    | varchar(20)   | yes  |     | null    |       |
| createtime   | date          | yes  |     | null    |       |
| ordermoney   | decimal(10,2) | yes  |     | null    |       |
| ordernumbers | int(4)        | yes  |     | null    |       |
+--------------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

特别说明：change 和 modify 都可以修改表的定义，不同的是 change 后面需要写两次列名，不方便。但是 change 的优点是可以修改列名称，modify 则不能。

3.3、增加表字段命令

alter table tablename add [column] column_definition [first | after col_name]

例：表 orders 上新增加字段 username，类型为 varchar(3) ：

mysql> alter table orders add column username varchar(30);
query ok, 0 rows affected (0.39 sec)
records: 0  duplicates: 0  warnings: 0

mysql> desc orders;
+-------------+---------------+------+-----+---------+-------+
| field       | type          | null | key | default | extra |
+-------------+---------------+------+-----+---------+-------+
| ordername   | varchar(20)   | yes  |     | null    |       |
| createtime  | date          | yes  |     | null    |       |
| ordermoney  | decimal(10,2) | yes  |     | null    |       |
| ordernumber | int(2)        | yes  |     | null    |       |
| username    | varchar(30)   | yes  |     | null    |       |
+-------------+---------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

3.4、删除表列字段命令

alter table tablename drop [column] col_name

例：表 orders 上删除字段 username：

mysql> alter table orders drop column username;
query ok, 0 rows affected (0.53 sec)
records: 0  duplicates: 0  warnings: 0

mysql> desc orders;
+-------------+---------------+------+-----+---------+-------+
| field       | type          | null | key | default | extra |
+-------------+---------------+------+-----+---------+-------+
| ordername   | varchar(20)   | yes  |     | null    |       |
| createtime  | date          | yes  |     | null    |       |
| ordermoney  | decimal(10,2) | yes  |     | null    |       |
| ordernumber | int(2)        | yes  |     | null    |       |
+-------------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

3.5、表改名命令

alter table tablename rename [to] new_tablename

例：表 orders 名字改为goodsorders

mysql> alter table orders rename goodsorders;
query ok, 0 rows affected (0.16 sec)

mysql> desc orders;
error 1146 (42s02): table 'ordermanage.orders' doesn't exist
mysql> desc goodsorders;
+--------------+---------------+------+-----+---------+-------+
| field        | type          | null | key | default | extra |
+--------------+---------------+------+-----+---------+-------+
| ordername    | varchar(20)   | yes  |     | null    |       |
| createtime   | date          | yes  |     | null    |       |
| ordermoney   | decimal(10,2) | yes  |     | null    |       |
| ordernumbers | int(4)        | yes  |     | null    |       |
+--------------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
 

4、dml 语句

插入（insert）、查询（select）、更新（update）、删除（delete）

4.1、插入记录 命令

insert into tablename (field1,field2,……fieldn) values(value1,value2,……valuesn);

例：表 goodsorders 中插入一条记录，ordername 为zhang，createtime为2021-05-12，ordermoney为100.00,ordernumbers为：1

mysql> insert into goodsorders (ordername,createtime,ordermoney,ordernumbers) values('zhang','2021-05-12',100.00,1);
query ok, 1 row affected (0.03 sec)

也可以省略(field1,field2,……fieldn)这一部分

mysql> insert into goodsorders  values('zhang1','2021-05-12',1001.00,11);
query ok, 1 row affected (0.05 sec)

4.2、查看插入数据命令

4.2.1、查询全部

select * from tablename [where condition]

例：查看goodsorders中所有插入数据

mysql> select * from goodsorders;
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| zhang     | 2021-05-12 |     100.00 |            1 |
| zhang1    | 2021-05-12 |    1001.00 |           11 |
+-----------+------------+------------+--------------+
2 rows in set (0.00 sec)

其中“*”表示要将所有的记录都选出来

4.2.2、查询不重复记录命令关键字

distinct

例：查询非goodsorders中非重复创建时间（createtime）的数据

mysql> select  * from goodsorders;
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| zhang     | 2021-03-11 |      50.00 |            1 |
| li        | 2020-05-12 |      70.00 |           15 |
| li        | 2020-03-12 |      70.00 |           15 |
| li        | 2020-03-11 |      70.00 |           15 |
| li        | 2021-03-11 |      70.00 |           15 |
+-----------+------------+------------+--------------+
5 rows in set (0.00 sec)

mysql> select distinct createtime from goodsorders;
+------------+
| createtime |
+------------+
| 2021-03-11 |
| 2020-05-12 |
| 2020-03-12 |
| 2020-03-11 |
+------------+
4 rows in set (0.00 sec)

由此可以看到，将重复的一条时间数据2021-03-11去掉了

4.2.3、多条件查询关键字

where 后面的条件是一个字段的‘='比较，还可以使用>、<、>=、<=、!=等比较运算符；
多个条件之间还可以使用 or、and 等逻辑运算符进行多条件联合查询，

例：查询非goodsorders中 ordername='li'并且createtime为2020-03-11

mysql> select * from goodsorders where ordername='li'and createtime ='2020-03-11';
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| li        | 2020-03-11 |      70.00 |           15 |
+-----------+------------+------------+--------------+
1 row in set (0.00 sec)

4.2.4、排序查询命名

select * from tablename [where condition] [order by field1 [desc|asc] ， field2 
[desc|asc]，……fieldn [desc|asc]]

例：把 goodsorders表中的记录按照创建时间高低进行排序显示

mysql> select * from goodsorders order by createtime;
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| li        | 2020-03-11 |      70.00 |           15 |
| li        | 2020-03-12 |      70.00 |           15 |
| li        | 2020-05-12 |      70.00 |           15 |
| zhang     | 2021-03-11 |      50.00 |            1 |
| li        | 2021-03-11 |      70.00 |           15 |
+-----------+------------+------------+--------------+
5 rows in set (0.01 sec)

4.2.5、显示一部分，而不是全部，指令

select ……[limit offset_start,row_count]

offset_start 表示记录的起始偏移量
row_count 表示显示的行数

例如1：显示 goodsorders表中按照 createtiem 排序后的前 3 条记录：

mysql> select * from goodsorders order by createtime limit 3;
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| li        | 2020-03-11 |      70.00 |           15 |
| li        | 2020-03-12 |      70.00 |           15 |
| li        | 2020-05-12 |      70.00 |           15 |
+-----------+------------+------------+--------------+
3 rows in set (0.00 sec)

例如2：如果要显示 goodsorders表中按照 createtiem 排序后 从第二条记录开始，显示3条数据：

mysql> select * from goodsorders order by createtime limit 2,3;
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| li        | 2020-05-12 |      70.00 |           15 |
| zhang     | 2021-03-11 |      50.00 |            1 |
| li        | 2021-03-11 |      70.00 |           15 |
+-----------+------------+------------+--------------+
3 rows in set (0.00 sec)

4.2.6、统计数据，聚合指令

select [field1,field2,……fieldn] fun_name 
from tablename
[where where_contition]
[group by field1,field2,……fieldn
[with rollup]]
[having where_contition]

参数说明：

• 1、fun_name 表示要做的聚合操作，也就是聚合函数，常用的有 sum（求和）、count(*)（记录数）、max（最大值）、min（最小值）
• 2、group by 关键字表示要进行分类聚合的字段，比如要按照部门分类统计员工数量，部门就应该写在 group by 后面。
• 3、with rollup 是可选语法，表明是否对分类聚合后的结果进行再汇总。
• 4、having 关键字表示对分类后的结果再进行条件的过滤。
  

注意：having 和 where 的区别在于 having 是对聚合后的结果进行条件的过滤，而 where 是在聚合前就对记录进行过滤，如果逻辑允许，我们尽可能用 where 先过滤记录，这样因为结果集减小，将对聚合的效率大大提高，最后再根据逻辑看是否用 having 进行再过滤。

例1：查询统计goodsorders表中，记录总数

mysql> select count(1) from goodsorders;
+----------+
| count(1) |
+----------+
|        5 |
+----------+
1 row in set (0.00 sec)

例2：在此基础上，按照创建日期（createtime）进行分组统计

mysql> select createtime,count(1) from goodsorders group by createtime;
+------------+----------+
| createtime | count(1) |
+------------+----------+
| 2020-03-11 |        1 |
| 2020-03-12 |        1 |
| 2020-05-12 |        1 |
| 2021-03-11 |        2 |
+------------+----------+
4 rows in set (0.00 sec)

例3：在此基础上，既要按照创建日期（cretetime）进行分组统计，又要计算总数

mysql> select createtime,count(1) from goodsorders group by createtime with rollup;
+------------+----------+
| createtime | count(1) |
+------------+----------+
| 2020-03-11 |        1 |
| 2020-03-12 |        1 |
| 2020-05-12 |        1 |
| 2021-03-11 |        2 |
| null       |        5 |
+------------+----------+
5 rows in set (0.02 sec)

最有一行，null所展示的数字，就是总数

例4：按照创建日期（createtime）进行分组统计，并且数量大于1

mysql> select createtime,count(1) from goodsorders group by createtime having count(1)>1;
+------------+----------+
| createtime | count(1) |
+------------+----------+
| 2021-03-11 |        2 |
+------------+----------+
1 row in set (0.00 sec)

例5：查询goodsorders表中，订单金额（ordermoney）的总额、最低额、最高额

mysql> select * from goodsorders;
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| zhang     | 2021-03-11 |      50.00 |            1 |
| li        | 2020-05-12 |      70.00 |           15 |
| li        | 2020-03-12 |      70.00 |           15 |
| li        | 2020-03-11 |      70.00 |           15 |
| li        | 2021-03-11 |      70.00 |           15 |
+-----------+------------+------------+--------------+
5 rows in set (0.00 sec)

mysql> select sum(ordermoney),max(ordermoney),min(ordermoney) from goodsorders;
+-----------------+-----------------+-----------------+
| sum(ordermoney) | max(ordermoney) | min(ordermoney) |
+-----------------+-----------------+-----------------+
|          330.00 |           70.00 |           50.00 |
+-----------------+-----------------+-----------------+
1 row in set (0.02 sec)

4.2.7、表连接

• 1、左连接：包含所有的左边表中的记录甚至是右边表中没有和它匹配的记录；关键指令：left join
• 2、右连接：包含所有的右边表中的记录甚至是左边表中没有和它匹配的记录；关联指令：right join

 例1：现在我们又创建一张用户表（member）,使用goodorders进行左连接，查询关联的用户表信息

mysql> select * from member;
+------+------------+
| id   | membername |
+------+------------+
| 15   | zhang      |
| 1    | li         |
| 13   | liss       |
+------+------------+
3 rows in set (0.00 sec)

mysql> select * from goodsorders;
+-----------+------------+------------+--------------+----------+
| ordername | createtime | ordermoney | ordernumbers | memberid |
+-----------+------------+------------+--------------+----------+
| zhang     | 2021-03-11 |      50.00 |            1 | 15       |
| li        | 2020-05-12 |      70.00 |           15 | 1        |
| li        | 2020-03-12 |      70.00 |           15 | 1        |
| li        | 2020-03-11 |      70.00 |           15 | 3        |
| li        | 2021-03-11 |      70.00 |           15 | 1        |
+-----------+------------+------------+--------------+----------+
5 rows in set (0.00 sec)

mysql> select * from goodsorders left join member on goodsorders.memberid = member.id;
+-----------+------------+------------+--------------+----------+------+------------+
| ordername | createtime | ordermoney | ordernumbers | memberid | id   | membername |
+-----------+------------+------------+--------------+----------+------+------------+
| zhang     | 2021-03-11 |      50.00 |            1 | 15       | 15   | zhang      |
| li        | 2020-05-12 |      70.00 |           15 | 1        | 1    | li         |
| li        | 2020-03-12 |      70.00 |           15 | 1        | 1    | li         |
| li        | 2021-03-11 |      70.00 |           15 | 1        | 1    | li         |
| li        | 2020-03-11 |      70.00 |           15 | 3        | null | null       |
+-----------+------------+------------+--------------+----------+------+------------+
5 rows in set (0.00 sec)

 例2：member和goodsorders中数据不变，我们再来看一下右连接的查询，以及结果：

mysql> select * from goodsorders right join member on goodsorders.memberid = member.id;
+-----------+------------+------------+--------------+----------+------+------------+
| ordername | createtime | ordermoney | ordernumbers | memberid | id   | membername |
+-----------+------------+------------+--------------+----------+------+------------+
| zhang     | 2021-03-11 |      50.00 |            1 | 15       | 15   | zhang      |
| li        | 2020-05-12 |      70.00 |           15 | 1        | 1    | li         |
| li        | 2020-03-12 |      70.00 |           15 | 1        | 1    | li         |
| li        | 2021-03-11 |      70.00 |           15 | 1        | 1    | li         |
| null      | null       |       null |         null | null     | 13   | liss       |
+-----------+------------+------------+--------------+----------+------+------------+
5 rows in set (0.00 sec)

这里发生了翻转，变为左侧goodsorders 表中的一条数据为空了

4.2.8、子查询，相关关键字

主要包括 in、not in、=、!=、exists、not exists 等

例：从goodsorders表中查询所有用户在memeber表中的记录

mysql> select * from member;
+------+------------+
| id   | membername |
+------+------------+
| 15   | zhang      |
| 1    | li         |
| 13   | liss       |
+------+------------+
3 rows in set (0.00 sec)

mysql> select * from goodsorders;
+-----------+------------+------------+--------------+----------+
| ordername | createtime | ordermoney | ordernumbers | memberid |
+-----------+------------+------------+--------------+----------+
| zhang     | 2021-03-11 |      50.00 |            1 | 15       |
| li        | 2020-05-12 |      70.00 |           15 | 1        |
| li        | 2020-03-12 |      70.00 |           15 | 1        |
| li        | 2020-03-11 |      70.00 |           15 | 3        |
| li        | 2021-03-11 |      70.00 |           15 | 1        |
+-----------+------------+------------+--------------+----------+
5 rows in set (0.00 sec)

mysql> select * from goodsorders where memberid in(select id from member);
+-----------+------------+------------+--------------+----------+
| ordername | createtime | ordermoney | ordernumbers | memberid |
+-----------+------------+------------+--------------+----------+
| zhang     | 2021-03-11 |      50.00 |            1 | 15       |
| li        | 2020-05-12 |      70.00 |           15 | 1        |
| li        | 2020-03-12 |      70.00 |           15 | 1        |
| li        | 2021-03-11 |      70.00 |           15 | 1        |
+-----------+------------+------------+--------------+----------+
4 rows in set (0.05 sec)

4.2.9、记录联合，指令

select * from t1
union|union all
select * from t2
……
union|union all
select * from tn;

union 和 union all 的主要区别：

   　　union all 是把结果集直接合并在一起，
　　   union 是将union all 后的结果进行一次 distinct，去除重复记录后的结果。

例1：将member表和goodsorders表中的用户编号id（memberid）的集合显示出来

mysql> select memberid from goodsorders union all select id from member;
+----------+
| memberid |
+----------+
| 15       |
| 1        |
| 1        |
| 3        |
| 1        |
| 15       |
| 1        |
| 13       |
+----------+
8 rows in set (0.00 sec)

例2：如果希望将上面的结果去掉重复记录后显示

mysql> select memberid from goodsorders union select id from member;
+----------+
| memberid |
+----------+
| 15       |
| 1        |
| 3        |
| 13       |
+----------+
4 rows in set (0.00 sec)

4.3、更新记录命令

update tablename set field1=value1，field2.=value2，……fieldn=valuen [where condition]

例：将表 goodsorders 中ordername为zhang的订单金额（ordermoney）改为50

mysql> update goodsorders set ordermoney=50.00 where ordername='zhang';
query ok, 1 row affected (0.09 sec)
rows matched: 1  changed: 1  warnings: 0

mysql> select * from goodsorders;
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| zhang     | 2021-05-12 |      50.00 |            1 |
| zhang1    | 2021-05-12 |    1001.00 |           11 |
+-----------+------------+------------+--------------+
2 rows in set (0.00 sec)

更新时，如遇到错误代码1175：

error code: 1175. you are using safe update mode and you tried to update a table without a where that uses a key column. to disable safe mode, toggle the option in preferences

解决方法：

1、先进行状体查询：

show variables like 'sql_safe_updates';

2、执行下面的sql，关闭safe-updates模式：

set sql_safe_updates = 0;

或者

set sql_safe_updates = false;
 

4.4、删除记录命名

delete from tablename [where condition]

例：将表 goodsorders 中ordername为zhang1的记录全部删除

mysql> delete from goodsorders where ordername = 'zhang1';
query ok, 1 row affected (0.06 sec)

mysql> select * from goodsorders;
+-----------+------------+------------+--------------+
| ordername | createtime | ordermoney | ordernumbers |
+-----------+------------+------------+--------------+
| zhang     | 2021-05-12 |      50.00 |            1 |
+-----------+------------+------------+--------------+
1 row in set (0.02 sec)
 

4.5、初始化表

例：将表中的所有数据清空

mysql> select * from varc;
+------+------+
| v    | c    |
+------+------+
| abc  | abc  |
+------+------+
1 row in set (0.03 sec)

mysql> truncate table varc;
query ok, 0 rows affected (0.25 sec)

mysql> select * from varc;
empty set (0.00 sec)
 

5、dcl 语句

dcl语句主要是为了管理数据库系统中的操作对象权限

5.1创建数据库用户

例：创建一个数据库用户 user1,初始密码为123，具有对 ordermanage 数据库中所有表的 select/insert 权限：

mysql> grant select,insert on ordermanage.* to 'user1'@'localhost' identified by '123';
query ok, 0 rows affected, 1 warning (0.06 sec)

mysql> exit
bye


c:\program files\mysql\mysql server 5.7\bin>mysql -uuser1 -p123
mysql: [warning] using a password on the command line interface can be insecure.
welcome to the mysql monitor.  commands end with ; or \g.
your mysql connection id is 82
server version: 5.7.17-log mysql community server (gpl)

copyright (c) 2000, 2016, oracle and/or its affiliates. all rights reserved.

oracle is a registered trademark of oracle corporation and/or its
affiliates. other names may be trademarks of their respective
owners.

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

mysql> show databases;
+--------------------+
| database           |
+--------------------+
| information_schema |
| ordermanage        |
+--------------------+
2 rows in set (0.00 sec)

在此基础上，将此用户（user1）的insert权限进行收回

mysql> revoke insert on ordermanage.* from 'user1'@'localhost';
query ok, 0 rows affected (0.02 sec)

mysql> exit
bye

c:\program files\mysql\mysql server 5.7\bin>mysql -uuser1 -p123
mysql: [warning] using a password on the command line interface can be insecure.
welcome to the mysql monitor.  commands end with ; or \g.
your mysql connection id is 84
server version: 5.7.17-log mysql community server (gpl)

copyright (c) 2000, 2016, oracle and/or its affiliates. all rights reserved.

oracle is a registered trademark of oracle corporation and/or its
affiliates. other names may be trademarks of their respective
owners.

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

mysql> use ordermanage;
database changed

mysql> insert into member values('11','ss');
error 1142 (42000): insert command denied to user 'user1'@'localhost' for table 'member'
mysql>

由此可以看出插入权限不足，插入失败

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