MySQL子查询与HAVING/SELECT的结合使用

SELECT deptno,COUNT(deptno) cnt,AVG(sal) avgsal 
FROM emp 
GROUP BY deptno
HAVING avgsal>
(
	SELECT AVG(sal) FROM emp
);

SELECT e.deptno,d.dname,ROUND(AVG(sal),2) avgsal
FROM emp e,dept d
WHERE e.deptno=d.deptno
GROUP BY e.deptno
HAVING avgsal>
(
    #查询出所有部门平均工资中最高的薪资
	 SELECT MAX(avgsal) FROM 
		(SELECT AVG(sal) avgsal FROM emp GROUP BY deptno) AS temp
)

#1多表查询
SELECT d.deptno,d.dname,d.loc,COUNT(e.deptno),AVG(e.sal)
FROM emp e,dept d
WHERE e.deptno=d.deptno
GROUP BY e.deptno;
#2
SELECT d.deptno,d.dname,d.loc,temp.cnt,temp.avgsal
FROM dept d,(SELECT deptno,COUNT(deptno) cnt,AVG(sal) avgsal FROM emp GROUP BY deptno) temp
WHERE d.deptno=temp.deptno;
#3 关联子查询
SELECT d.deptno,d.dname,d.loc,
(SELECT COUNT(deptno) FROM emp WHERE deptno=d.deptno GROUP BY deptno) cnt,
(SELECT AVG(sal) FROM emp WHERE deptno=d.deptno GROUP BY deptno) avgsal
FROM dept d;

SELECT e.deptno,e.ename,e.sal
FROM emp e
WHERE e.sal>(SELECT AVG(sal) FROM emp WHERE deptno=e.deptno );

-- 多表查询
SELECT d.deptno,d.dname,d.loc,AVG(e.sal) avgsal ,COUNT(e.deptno) cnt
FROM dept d,emp e
WHERE d.deptno=e.deptno
GROUP BY e.deptno;
-- 子查询
SELECT d.deptno,d.dname,d.loc,temp.avgsal,temp.cnt
FROM dept d,(
							SELECT deptno,AVG(sal) avgsal,COUNT(deptno) cnt
							FROM emp
							GROUP BY deptno
						)temp
WHERE d.deptno=temp.deptno;
-- 使用with
WITH temp AS(
							SELECT deptno,AVG(sal) avgsal,COUNT(deptno) cnt
							FROM emp
							GROUP BY deptno
						)
SELECT d.deptno,d.dname,d.loc,temp.avgsal,temp.cnt
FROM dept d,temp
WHERE d.deptno=temp.deptno;

-- 相关子查询
SELECT e.empno,e.ename,e.job,e.hiredate,e.sal,e.deptno,d.dname
FROM emp e,dept d
WHERE e.deptno=d.deptno
AND e.sal=(SELECT MAX(sal) FROM emp WHERE deptno=e.deptno)
ORDER BY e.deptno;
-- 表子查询
SELECT e.empno,e.ename,e.job,e.hiredate,e.sal,e.deptno,d.dname
FROM emp e,dept d,(SELECT deptno,MAX(sal) maxsal FROM emp GROUP BY deptno) temp
WHERE e.deptno=d.deptno
AND e.sal=temp.maxsal
AND e.deptno = temp.deptno
ORDER BY e.deptno;

-- 多表查询
SELECT DISTINCT e.empno,e.ename,e.job,e.deptno
FROM emp e JOIN emp mgr
ON e.empno=mgr.mgr;
-- 使用EXISTS
SELECT e.empno,e.ename,e.job,e.deptno
FROM emp e
WHERE EXISTS (SELECT * FROM emp WHERE e.empno=mgr);

-- 多表查询
SELECT e.deptno,d.deptno,d.dname,d.loc
FROM emp e RIGHT JOIN dept d
ON e.deptno=d.deptno
WHERE e.deptno IS NULL;
-- 使用EXISTS
SELECT d.deptno,d.dname,d.loc
FROM  dept d
WHERE NOT EXISTS (SELECT deptno FROM emp WHERE deptno=d.deptno);