SQL语句的一些应用语句

show databases;
show variables like '%char%';
--  创建数据库的sql
create database if not exists study charset =utf8;
use develop;

show tables;

-- 删除数据库的sql
drop database if exists develop;

-- 创建一个用户
create user 'develop'@'%' identified by 'sa';
-- 删除一个用户
drop user 'develop'@'%';
-- 给develop用户赋予对develop数据的所有表的权限
grant all privileges on develop.* to 'develop'@'%' identified by 'sa';



insert into mysql.user(Host,User,Password,ssl_cipher, x509_issuer,x509_subject)
values('%', 'develop', password('sa'),'','','');

update mysql.user set Password=Password('1') where user = 'develop' and host ='%';

select host,user, Password from mysql.user;

delete from mysql.user where user = 'develop' and host ='%';

use study;

-- 创建表
create table student(
  sno int,
  name varchar(10),
  age int,
  sex char(1)
);
-- 删除表
drop table student;

-- 创建带有自增主键的表
create table student(
  id int unsigned auto_increment,
  name varchar(10),
  age int,
  gender char(1),
  primary key (id)
);

-- 添加classname字段
alter table study.student
  add (
    classname varchar(100)
  );

-- 修改gender列的长度
alter table study.student
  modify gender char(2);

-- 修改gender列为sex，长度增加为10
alter table study.student
    change gender sex char(10);

-- 删除列
alter table study.student
    drop classname;

-- 修改表名
alter table study.student
    rename to stu;

show create table stu;

-- 在stu表中插入一个学生记录
insert into stu(name, age, sex) values('zhangsan', 20, 'male');

select * from stu;

insert into stu(name) values('lisi');
insert into stu(id, name) values(3, 'xiaoer');
insert into stu(id, name) values(3, 'xiaoming');
insert into stu(sex, name, age, id) values('male', 'xiaohong', 3, 4);

-- 在stu表中插入行的另外一种写法
-- 不建议使用此方式：1) 列不明确。2)当表有新增的列时，会产生毁灭性的bug
insert into stu values (5, 'wangwu', 20, 'male');

alter table stu modify name varchar(20);

-- 通过update语句修改记录
update stu set name='zhangsansan', age = 25 where id = 1;

-- between 条件
update stu set age = age + 1 where age between 10 and 20;

-- 上机练习
-- 创建一个学生表:
create table student(
  id char(6),
  name varchar(50),
  age int,
  gender varchar(50),
  tag varchar(2)
);

-- 插入测试数据
INSERT INTO student VALUES('S_1001', 'liuYi', 35, 'male', '');
INSERT INTO student VALUES('S_1002', 'chenEr', 15, 'female', '');
INSERT INTO student VALUES('S_1003', 'zhangSan', 95, 'male', '');
INSERT INTO student VALUES('S_1004', 'liSi', 65, 'female', '');
INSERT INTO student VALUES('S_1005', 'wangWu', 55, 'male', '');
INSERT INTO student VALUES('S_1006', 'zhaoLiu', 75, 'female', '');

-- 1. 将为'S_1003'的学生的年龄改为25
update study.student set age = 25 where id = 'S_1003';

-- 2. 将'wangwu'的性别改成NULL
update study.student set gender = null where name = 'wangWu' or id = 'S_1005';

-- 3. 将年龄大于等于35岁的人标记成'1'
update study.student set tag = '1' where age >= 35;

-- 4. 将年龄大于等于15岁小于35岁的人标记成'0'
update study.student set tag = '0' where age >= 15 and age < 35;

-- 删除语句
delete from study.student where id = 'S_1001' and gender = 'famale';
delete from study.student;

-- 截断：清空student表的所有数据，无法恢复
truncate table student;

-- 查询示例
-- 创建员工表
CREATE TABLE emp(
	empno		INT,/*员工编号*/
	ename		VARCHAR(50),/*员工名称*/
	job		VARCHAR(50),/*工作职位*/
	mgr		INT,/*管理编号*/
	hiredate	DATE,/*入职时间*/
	sal		DECIMAL(7,2),/**薪酬/
	comm		decimal(7,2),/*奖金*/
	deptno		INT/*部门编号*/
);
drop table dept;
alter table dept default character set utf8;/*修改表编码格式为utf8*/
alter table dept convert to character set utf8;/*修改列属性的格式为utf8*/

SHOW FULL COLUMNS FROM dept;/*查看dept表的编码格式*/
-- 创建部门表
CREATE TABLE dept(
	deptno		INT  ,/*部门编号*/
	dname		varchar(40) , /*部门名称*/
	loc		varchar(40)   /*工作地*/
);
-- 插入员工表测试数据
INSERT INTO emp VALUES (1009, 'zenganiu', 'chairman', NULL, '2001-11-17', 50000, NULL, 10);
INSERT INTO emp VALUES (1004, 'liubei', 'manager', 1009, '2001-04-02', 29750, NULL, 20);
INSERT INTO emp VALUES (1006, 'guanyu', 'manager', 1009, '2001-05-01', 28500, NULL, 30);
INSERT INTO emp VALUES (1007, 'zhangfei', 'manager', 1009, '2001-09-01', 24500, NULL, 10);
INSERT INTO emp VALUES (1008, 'zhugeliang', 'analyst', 1004, '2007-04-19', 30000, NULL, 20);
INSERT INTO emp VALUES (1013, 'pangtong', 'analyst', 1004, '2001-12-03', 30000, NULL, 20);
INSERT INTO emp VALUES (1002, 'daiyisi', 'salesman', 1006, '2001-02-20', 16000, 3000, 30);
INSERT INTO emp VALUES (1003, 'yintianzheng', 'salesman', 1006, '2001-02-22', 12500, 5000, 30);
INSERT INTO emp VALUES (1005, 'xiexun', 'salesman', 1006, '2001-09-28', 12500, 14000, 30);
INSERT INTO emp VALUES (1010, 'weiyixiao', 'salesman', 1006, '2001-09-08', 15000, 0, 30);
INSERT INTO emp VALUES (1012, 'chengpu', 'clerk', 1006, '2001-12-03', 9500, NULL, 30);
INSERT INTO emp VALUES (1014, 'huanggai', 'clerk', 1007, '2002-01-23', 13000, NULL, 10);
INSERT INTO emp VALUES (1011, 'zhoutai', 'clerk', 1008, '2007-05-23', 11000, NULL, 20);
INSERT INTO emp VALUES (1001, 'ganning', 'clerk', 1013, '2000-12-17', 8000, NULL, 20);

-- 插入部门表测试数据
INSERT INTO dept (deptno,dname,loc)VALUES (10, '企划部', '北京');
INSERT INTO dept (deptno,dname,loc)VALUES (20, '公关部', '上海');
INSERT INTO dept (deptno,dname,loc)VALUES (30, '销售部', '广州');
INSERT INTO dept (deptno,dname,loc)VALUES (40, '财务部', '武汉');

-- 基础查询
select * from emp;
-- 指定列查询
select empno, ename from emp;

-- distinct 对查询出的记录去重
select distinct job from emp;
select distinct deptno from emp;
select distinct job, deptno from emp;

-- 列运算
select *, sal * 1.5 from emp;
select *, sal + comm from emp;

-- null值转换函数：ifnull(field, value)
select *, sal + IFNULL(comm, 0) from emp;
select empno,ename,job,ifnull(mgr,'boss'),hiredate,sal,comm,deptno from emp;

-- 字符串连接
select concat('$', sal) from emp;
select concat(ename, job) from emp;
select concat('my name is ', ename, ' my job is ', job) from emp;

-- 给列起别名
select concat('my name is ', ename, ' my job is ', job) as name_job from emp;
select *, sal + IFNULL(comm, 0) as 奖金 from emp;
select ename as 姓名 from emp;

-- 条件查询
select empno,ename,sal,comm from emp where sal > 10000 and comm is not null;
select empno,ename,sal,comm from emp where sal between 20000 and 30000;
select empno,ename,sal,comm from emp where job in ('chairman', 'manager');

-- 模糊查询
SELECT * FROM emp WHERE ename LIKE 'z_______';
select * from emp where ename like '______';
select * from emp where ename like 'z%';
select * from emp where ename like '%z%';
select * from emp where ename like '_h%';
select * from emp where ename like '%n_';
use Student;
-- 排序,升序和降序，默认是升序，asc升序，desc降序
select * from emp order by empno;
select * from emp order by empno asc;
select * from emp order by empno desc;

-----复合函数
------count函数
select count(*)from emp;
select count(comm)from emp;
select count(*)from emp where sal >25000;
select count(*)from emp where sal +ifnull(comm)>25000;
select count(comm),count(mgr)from emp ;

/*sum函数*/
select sum(sal) from emp;
select sum(sal),sum(comm) from emp;
select sum(sal)+ifnull(comm,0)from emp;
select sum(sal)/count(*)from emp;
select sum(ename) from emp;

-------avg函数
select avg(sal)from emp;
select avg(ename)from emp;
---------max函数
select max(sal)from emp;
select max(ename)from emp;
select max(comm)from emp;

---------- -  min 函数
select min(sal)from emp;
select min(ename)from emp;
select min(comm)from emp;


-----------------union 函数
select max(sal)from emp;
union
select min(sal) from  emp;


select sum(sal),sum(comm)from emp;
union
select max(sal) from  emp;



select  * from emp;
union
select * from  emp;

select  * from emp;
union all
select * from  emp;

-----分组查询 group by

select  deptno, count(*) from emp group by deptno;
select job ,count(*) from emp group by  deptno;
select job ,sum(sal) from emp group by  job;
select job ,sum(sal) ,avg(sal),max(sal),min(sal)from emp group by job;
---------------组条件
-----------------分组前条件

select deptno ,count(*)from  emp where  sal>15000 group by  deptno;
----------------分组后条件
select deptno ,count(*)from  emp group by deptno having count(*)>3;
select deptno ,sum(sal) from  emp group by deptno having count(*)>3;
------分组后排序
select deptno ,count(*)from  emp where  sal>15000 group by  deptno having  count(*)>1 order by  deptno desc ;



/*第五条数据开始，往后查4条数据*/
select * from emp order by  empno limit  5,4;

/*分页查询*/
select  *from  emp order by  empno limit 5;
select  *from  emp order by  empno limit 0,5;/*从0开始，包括第一行，到第一行*/

/*一页5条，查询第三页的数据*/

select  *from emp order by empno limit 10,5;

select  * from emp order by empno limit 10 , 5;


/*
1、查询出部门编号为30的员工
2、查询出所有销售员的姓名、编号和部门编号
3、找出奖金高于工资的员工
4、找出奖金高于工资30%的员工
5、找出部门编号为10的所有经理，和部门编号为20中所有销售员的详细资料
*/

select * from emp where deptno=30;
select   ename,empno,deptno from emp where job='salesman';

select * from emp where comm>sal;
select * from  emp where comm>sal * 0.30;
select * from emp  where deptno =10 and job='manager'



1、找出部门编号为10中的所有经理，部门编号为20中所有销售员，还有即不是经理也不是销售员但其工资大或大于或等于20000的所有员工详细资料。
select  * from emp where deptno='10'and job='manager'
union
select * from emp where deptno ='20'and job='salesman'
union
select  *from emp where (job<>'manager'or job <>'salesman')and  sal >=200000;
2、无奖金或者奖金低于1000的员工

select *from emp where comm is null or comm<1000;
------3、查询名字由8个字符组成的员工
  select  *from emp where ename like '________';
4、查询2000年入职的员工

select  *from emp where year(hiredate)=2000;
5查询所有员工的详细信息，用编号升序排序。

select  *from emp order by empno ;

use Student

-- 插入部门表测试数据
INSERT INTO dept VALUES (10, '企划部', '北京');
INSERT INTO dept VALUES (20, '公关部', '上海');
INSERT INTO dept VALUES (30, '销售部', '广州');
INSERT INTO dept VALUES (40, '财务部', '武汉');

INSERT INTO dept VALUES (10, '企划部', '北京');
INSERT INTO dept VALUES (20, '公关部', '上海');
INSERT INTO dept VALUES (30, '销售部', '广州');
INSERT INTO dept VALUES (40, '财务部', '武汉');

/*我们要取出员工工号，姓名、部门名称  、入职时间、等信息；该如何取*/
select emp.empno , emp.ename, dept.dname,emp.hiredate from emp inner join  dept on emp.deptno=dept.deptno;

等价于
select  emp.empno,emp.ename,dept.dname,emp.hiredate from emp, dept where emp.deptno=dept.deptno;


select  *from emp order by empno ;

show full  columns from dept;


------left join
select empno,ename,dname,hiredate from emp left join  dept on emp.deptno =dept.deptno;
------ right join
select  empno ,ename,dname,hiredate from emp right join dept on emp.deptno =dept.deptno;


----子查询：在另一条是 select 作为条件
select *from emp where deptno in (select  deptno from dept where loc='北京');
select *from emp where not  exists(select  deptno from dept where loc='北京'and dept.deptno=emp.deptno);

------1、查询出部门内所有员工薪酬低于20000的员工的部门名称及位置；
select dname ,loc from dept where  deptno in(select deptno from emp where  sal<20000);


select dname ,loc from dept where  deptno in(select deptno from emp group by emp.deptno having  max(sal)<20000) ;


2、查询‘武汉’地区所有员工的工作（job）;

select job from  emp where  deptno in (select  deptno from dept where  loc='武汉');


3、查询所有job 不为‘chairman’的员工的工号、姓名、部门名称和办公地址；

select  empno,ename ,dname,loc from emp left join  dept on  emp.deptno =dept.deptno where job  <>'chairman';
===更高效的写法
select  empno,ename ,dname,loc from emp left join  dept on  emp.deptno =dept.deptno where not exists(select  1 from  emp e where e.empno=emp.empno and job ='chairman') ;

本文地址：https://blog.csdn.net/weixin_43501566/article/details/108568912