MySql数据库练习

-- 员工信息表
CREATE TABLE emp( empno INT, ename VARCHAR(50), job VARCHAR(50), mgr INT,
hiredate DATE, sal DECIMAL(7,2), comm DECIMAL(7,2), deptno INT ) ;
INSERT INTO emp values(7369,'SMITH','CLERK',7902,'1980-12-17',800,NULL,20);
INSERT INTO emp values(7499,'ALLEN','SALESMAN',7698,'1981-02-20',1600,300,30);
INSERT INTO emp values(7521,'WARD','SALESMAN',7698,'1981-02-22',1250,500,30);
INSERT INTO emp values(7566,'JONES','MANAGER',7839,'1981-04-02',2975,NULL,20);
INSERT INTO emp values(7654,'MARTIN','SALESMAN',7698,'1981-09-28',1250,1400,30);
INSERT INTO emp values(7698,'BLAKE','MANAGER',7839,'1981-05-01',2850,NULL,30);
INSERT INTO emp values(7782,'CLARK','MANAGER',7839,'1981-06-09',2450,NULL,10);
INSERT INTO emp values(7788,'SCOTT','ANALYST',7566,'1987-04-19',3000,NULL,20);
INSERT INTO emp values(7839,'KING','PRESIDENT',NULL,'1981-11-17',5000,NULL,10);
INSERT INTO emp values(7844,'TURNER','SALESMAN',7698,'1981-09-08',1500,0,30);
INSERT INTO emp values(7876,'ADAMS','CLERK',7788,'1987-05-23',1100,NULL,20);
INSERT INTO emp values(7900,'JAMES','CLERK',7698,'1981-12-03',950,NULL,30);
INSERT INTO emp values(7902,'FORD','ANALYST',7566,'1981-12-03',3000,NULL,20);
INSERT INTO emp values(7934,'MILLER','CLERK',7782,'1982-01-23',1300,NULL,10);
INSERT INTO emp values(7981,'MILLER','CLERK',7788,'1992-01-23',2600,500,20);
-- 部门信息表
CREATE TABLE dept( deptno INT, dname varchar(14), loc varchar(13) );
INSERT INTO dept values(10, 'ACCOUNTING', 'NEW YORK');
INSERT INTO dept values(20, 'RESEARCH', 'DALLAS');
INSERT INTO dept values(30, 'SALES', 'CHICAGO');
INSERT INTO dept values(40, 'OPERATIONS', 'BOSTON');

查询
--所有员工的信息
SELECT * FROM emp
--薪资大于等于1000并且小于等于2000的员工信息
SELECT * FROM emp WHERE sal>=1000 and sal<=2000
--从员工表中查询出所有的部门编号
SELECT DISTINCT deptno FROM emp
--查询出名字以A开头的员工的信息
SELECT * FROM emp WHERE ename LIKE 'A%'
--查询出名字第二个字母是L的员工信息
SELECT * FROM emp WHERE ename LIKE '_L%'
--查询出没有奖金的员工信息
SELECT * FROM emp WHERE comm IS NULL OR comm = 0
--所有员工的平均工资
SELECT AVG(sal) FROM emp
--所有员工的工资总和
SELECT SUM(sal) FROM emp
--所有员工的数量
SELECT COUNT(empno) FROM emp
--最高工资
SELECT MAX(sal) FROM emp
--最少工资
SELECT MIN(sal) FROM emp
--最高工资的员工信息
SELECT * FROM emp WHERE SAL=(SELECT MAX(sal) FROM emp)
--最低工资的员工信息
SELECT * FROM emp WHERE sal=(SELECT MIN(sal) FROM emp)
--每个部门的平均工资
SELECT AVG(sal) FROM emp GROUP BY deptno

子查询
-- 单行子查询(> < >= <= = <>)
-- 查询出高于10号部门的平均工资的员工信息
SELECT * FROM emp WHERE sal>(SELECT AVG(SAL) FROM emp WHERE deptno=10)
-- 多行子查询(in not in any all) >any >all
-- 查询出比10号部门任何员工薪资高的员工信息
select * from emp where sal > any(select sal from emp where deptno=10);
-- 多列子查询(实际使用较少) in
-- 和10号部门同名同工作的员工信息
SELECT * FROM emp WHERE ename in (SELECT ename FROM emp WHERE deptno=10) AND job in (SELECT job FROM emp WHERE deptno=10) AND deptno IS NOT '10'
-- Select接子查询
-- 获取员工的名字和部门的名字
SELECT e.ename,d.dname FROM emp e join dept d on e.deptno=d.deptno
-- from后面接子查询
-- 查询emp表中经理信息
select * from emp where job='MANAGER';
-- where 接子查询
-- 薪资高于10号部门平均工资的所有员工信息
SELECT * FROM emp WHERE sal>(SELECT AVG(sal) FROM emp WHERE deptno=10)
-- having后面接子查询
-- 有哪些部门的平均工资高于30号部门的平均工资
SELECT deptno FROM emp GROUP BY deptno HAVING AVG(sal)>(SELECT AVG(sal) FROM emp WHERE deptno=30)
-- 工资>JONES工资
SELECT * FROM emp WHERE sal > (SELECT sal FROM emp WHERE ename = 'JONES')
-- 查询与SCOTT同一个部门的员工
SELECT * FROM emp WHERE deptno = (SELECT deptno FROM emp WHERE ename = 'SCOTT')
-- 工资高于30号部门所有人的员工信息
SELECT * FROM emp WHERE sal > ALL(SELECT sal FROM emp WHERE deptno = 30)
-- 查询工作和工资与MARTIN完全相同的员工信息
SELECT * FROM emp WHERE (job,sal) in (SELECT job,sal FROM emp WHERE ename = 'MARTIN')
-- 有两个以上直接下属的员工信息
SELECT * FROM emp GROUP BY mgr HAVING COUNT(*)>2
-- 查询员工编号为7788的员工名称,员工工资,部门名称,部门地址
SELECT e.ename,e.sal,d.dname,d.loc FROM emp e JOIN dept d on e.deptno=d.deptno where empno=7788

SQL查询的综合案例
1. 查询出高于本部门平均工资的员工信息
SELECT * FROM emp e WHERE sal > (SELECT AVG(sal) FROM emp ee GROUP BY deptno HAVING e.deptno=ee.deptno)
2. 列出达拉斯加工作的人中,比纽约平均工资高的人
SELECT * FROM emp WHERE deptno=20 and sal > (SELECT AVG(sal) FROM emp WHERE deptno=10)
3. 查询7369员工编号,姓名,经理编号和经理姓名
SELECT e.empno,e.ename,d.empno,d.ename FROM emp e,emp d WHERE e.mgr=d.empno AND e.empno=7369;
4. 查询出各个部门薪水最高的员工所有信息
SELECT e.empno,e.ename,e.job,e.mgr,e.hiredate,e.sal,e.comm,e.deptno,d.dname,d.loc FROM emp e,dept d where sal=(SELECT MAX(sal) FROM emp ee GROUP BY deptno HAVING e.deptno=ee.deptno) AND e.deptno=d.deptno