MySQL 复合查询案例详解

select * from emp where (salary>500 or job='MANAGER') and ename like 'J%';
select * from emp where (salary>500 or job='MANAGER') and substring(ename,1,1)='J';

select * from emp order by deptno asc,sal desc;

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

select ename,job from emp where sal=(select max(sal) from emp);

select * from emp where sal > (select avg(sal) from emp);

// 保留2位精度统计
select deptno,format(avg(sal),2),max(sal) where emp group by deptno;

// 分组有多个部门，每个部门的平均工资
// having对分组之后的结果进行判断
select deptno,avg(sal) 平均工资 from emp group by deptno having 平均工资 < 2000  

select job,count(job) 人数,format(avg(sal),2) 平均工资 from emp group by job;

// 连接两张表进行查询
select ename,sal,dname from dept,emp where emp.deptno=dept.deptno;

select ename,sal,dname,dept.deptno from emp,dept where emp.deptno=dept.deptno and emp.dpetno=10;

select ename,sal,grade,losal,hisal from emp,salgrade where sal between losal and hisal;

select ename,empno from emp where empno=(select mgr from emp where ename='FORD');

select e2.ename,e2.empno from emp e1,emp e2 where e1.ename='FORD' and e1.mgr=e2.empno;

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

select ename,job,sal,deptno from emp where job in(select distinct job from where deptno=10) and
deptno <> 10;

select ename,job,sal,dname from
(select ename,job,sal,deptno from emp where job in 
(select distinct job from emp where deptno=10) and deptno<>10;)
and deptno <>10) as tmp ,dept where dept.deptno=tmp.deptno;

select * from emp where sal > (select max(sal) from emp where deptno=30);

select * from emp where sal > any(select distinct sal from emp where deptno=30);

select * from emp where sal > any(select distinct sal from emp where deptno=30);

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

// 查询分组后的部门号和平均工资
select deptno,avg(sal) from emp group by dpetno;

// 对员工表和部门的平均工资表做拼接
// 做笛卡尔积要部门号相同才有意义
select * from emp,(select deptno,avg(sal) from emp group by deptno) as tmp where emp.deptno=tmp.deptno;

select * from emp,(select deptno,avg(sal) as myavg from emp group by deptno) as tmp where emp.deptno=tmp.deptno and emp.sal > tmp.myavg;

select ename,sal,t1.deptno,mymax from emp as t1,(select deptno,max(sal) mymax from emp group by deptno) as t2 where t1.deptno=t2.deptno and t1.sal=t2.mymax;

select t1.deptno,t1.dname,t1.loc,t2.dept_num from dept as t1,(select deptno,count(*) as dept_num from emp group by deptno) as t2 where t1.deptno=t2.deptno;

select DEPT.dname, DEPT.deptno, DEPT.loc,count(*) '部门人数' from EMP,
DEPT
where EMP.deptno=DEPT.deptno
group by DEPT.deptno,DEPT.dname,DEPT.loc;

select * from emp where sal>2500 union select * from emp where job='MANAGER'; 

select * from emp where sal > 25000 union select * from emp where job='MANAGER';