mysql数据库多表查询练习题[通俗易懂]

SELECT d.deptno,d.dname,d.loc,e1.`count(*)`
FROM dept d INNER JOIN (SELECT deptno,COUNT(*) FROM emp GROUP BY deptno) e1
ON d.deptno=e1.deptno;

SELECT *
FROM emp e
WHERE e.sal>(SELECT sal FROM emp WHERE ename='关羽')

SELECT e1.ename,e2.ename 上级
FROM emp e1 LEFT OUTER JOIN emp e2
ON e1.mgr=e2.empno;

SELECT  e1.empno,e1.ename,d.dname
FROM emp e1 LEFT OUTER JOIN emp e2 ON e1.mgr=e2.empno  
LEFT OUTER JOIN dept d ON e1.deptno=d.deptno
WHERE e1.hiredate<e2.hiredate

SELECT d.dname,e.*
FROM dept d LEFT OUTER JOIN emp e
ON d.deptno=e.deptno;

SELECT e.ename,d.dname,z.`count(*)`
FROM emp e INNER JOIN dept d ON e.deptno=d.deptno
	   INNER JOIN (SELECT deptno,COUNT(*) FROM emp GROUP BY deptno)z ON z.deptno=d.deptno
WHERE e.job='文员'

SELECT job,COUNT(*) 
FROM emp 
GROUP BY job 
HAVING MIN(sal)>15000

SELECT e1.ename
FROM emp e1 INNER JOIN dept d
ON e1.deptno=d.deptno
WHERE d.dname='销售部'

SELECT e1.*,e2.ename 上级,d.dname 部门名称,sal.`grade`
FROM emp e1 LEFT OUTER JOIN emp e2 ON e1.mgr=e2.empno
            LEFT OUTER JOIN dept d ON e1.deptno=d.deptno
            LEFT OUTER JOIN salgrade sal ON e1.sal BETWEEN losal AND hisal
WHERE e1.`sal`>(SELECT AVG(sal) FROM emp)

SELECT e.ename,d.dname
FROM emp e INNER JOIN dept d
ON e.deptno=d.deptno
WHERE e.job=(SELECT job FROM emp WHERE ename='庞统')

SELECT e.ename,e.sal,d.dname
FROM emp e LEFT OUTER JOIN dept d
ON e.deptno=d.deptno
WHERE e.sal>ALL(SELECT sal FROM emp WHERE deptno=30)

SELECT d.dname,e1.*
FROM (SELECT e.deptno,COUNT(*),AVG(sal) FROM emp e GROUP BY e.deptno)e1 INNER JOIN dept d
ON e1.deptno=d.deptno;

SELECT tb1.*,IFNULL(CONCAT((tb1.zz-tb2.zz)/tb2.zz*100,'%'),0) 年度增长比
FROM tbyear tb1 LEFT OUTER JOIN tbyear tb2
ON tb1.`year`=tb2.`year`+1;