6.复合查询

查询工资高于500或者岗位为manger的孤雁，同时满足首字母为大写J
select ename,sal job from emp where sal>500 or (job=manger and ename like 'J%')

select ename,deptno,sal from emp order by deptno ，sal desc;

select ename,sal*12+ifnull(comm,0) 年薪from deptno order by 年薪; 

select * from emp where sal=(select max(sal) from emp);

select name,sal where sal>(select avg(sal) from emp) order by sal;

select deptno, max(sal),avg(sal) from emp group by deptno;

select deptno,avg(sal) my_avg from emp group by deptno having my_avg<2000;

select job, count(*) person ,avg(sal)from emp group by(job); 

多表查询

select * from emp,dept;

selecft deptno,ename sal from emp,dept where dept.deptno=emp.deptno;

自连接

select* from emp ,emp emp_bak;

select ename,empno from emp worker,emp leader ehere worder.mgr=leader.empno and work.enmae='ford';

select * from emp where deptno=(select deptno from emp where ename='smith');

in关键字：
查询和10号部门的工作岗位的雇员的名字，岗位，工资，部门号，但是不包括自己
select ename,job,sal,deptno from emp where job in (select distinct job from emp where deptno=10) and deptno<>10;

all关键字:比所有人都...
显示工资比部门30的所有员工工资高的员工的姓名，工资和部门号
select ename,sgl,deptno from emp where sal> all(select distinct sal from emp where deptno=30 )

any关键字：比其中一个怎么咋们样
显示工资比部门30的任意员工工资高的员工的姓名，工资和部门号(包括自己部门的员工)
select ename,sal,deptno from emp where sal >any (select distinct sal from emp where deptno=30)

查询和SMITH的部门和岗位完全相同的所有雇员,不包括本人

select * from where (deptno,job) (select deptno,job from emp where ename='SMITH') and ename<>'SMITH';

查询和smith部门和岗位完全相同的所有雇员，不含Smith本人
select ename from EMP where (deptno,job)=select(deptno,job from EMP where ename='SMITH') and ename <> 'SMITH';

显示每个高于自己部门平均工资的员工的姓名，工资,部门，平均工资

select deptno,format(avg(sal),2) _avg from emp group by deptno;

select * from emp,(select deptno dt ,avg(sal) _avg from emp group by deptno) agv_tab where emp.dpetno=avg_tab.deptno and emp.sal>avg_tab._avg;

select ename,sal,deptno,_max from emp, select deptno dp,max(sal)  _max,from emp group by dt max_tb where emp.deptno=max_tb.dp and emp.sal=max_tb._max ;

select * from dept,select deptno,count(*) from emp group by deptno sub_table where  dept.deptno=sub_table.septno;

select ename from emp where sla>5000 or job='manger';

select ename,sal,job,from emp where sal>2500;
select ename,sal job from emp where job='manger'

union:上下两个表合并成一张表，去掉重复的内容
select ename,sal,job,from emp where sal>2500 union
select ename,sal job from emp where job='manger'
只要列数相同就可以

union all与union的区别是不会进行去重
select ename,sal,job,from emp where sal>2500 union all
select ename,sal job from emp where job='manger'

select 字段 from 表1 inner join 表2 on 连接条件 and 连接条件

select * from emp inner join dept on emp.deptno =dept.deptno;

显示SIMTH的名字和部门名
select * from emp,dept where emp.deptno=dept.deptno and emp.ename='SMITH';

select ename,dname from emp innor join dept on emp.deptno=dept.deptno;

select 字段名 from 表名1 left join 表名2 on 连接条件

-- 建两张表 
create table stu (id int, name varchar(30));-- 学生表
insert into stu values(1,'jack'),(2,'tom'),(3,'kity'),(4,'nono');、
create table exam (id int, grade int); -- 成绩表 
insert into exam values(1, 56),(2,76),(11, 8);

select * from stu left join exam  on stu.id=exam.id;
//如果这个学生没有成绩，也要讲这个学生的个人信息显示出来

select 字段 from 表1 right join 表名2 on 连接条件

对stu表和exam表联合查询，把所有的成绩显示出来，即使这个成绩没有学生与之对应也要显示出来
select * from stu right join exam on stu.id=exam.id;