MYSQL子查询练习

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);

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');

--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);

-- 单行子查询(> < >= <= = <>)
   -- 查询出高于10号部门的平均工资的员工信息
    1.10号部门的平均工资
    SELECT AVG(sal) FROM emp WHERE deptno = 10;
    2. 高于上面结果员工信息
   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
   1. 查询出10号部门最高工资
   SELECT MAX(sal) FROM emp WHERE deptno = 10;
   2. 得出结果
   SELECT * FROM emp WHERE sal > (SELECT MAX(sal) FROM emp WHERE deptno = 10);
   -- 查询出比10号部门任意一个员工薪资高的所有员工信息 : 只要比其中随便一个工资都可以
   SELECT sal FROM emp WHERE deptno = 10;

   SELECT * FROM emp WHERE sal >ANY(SELECT sal FROM emp WHERE deptno = 10) AND 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
   1. 查询出10号部门所有人名字和工作
   SELECT ename,job FROM emp WHERE deptno=10;
   2. 得出结果
   SELECT * FROM emp WHERE (ename,job) IN (SELECT ename,job FROM emp WHERE deptno=10) AND deptno !=10;
-- Select后面接子查询
   -- 获取员工的名字和部门的名字
   SELECT ename,deptno FROM emp ;

   SELECT ename,(SELECT dname FROM dept d WHERE d.deptno = e.deptno ) 部门名称 FROM emp e ;
-- from后面接子查询
   -- 查询emp表中所有管理层的信息
   SELECT DISTINCT mgr FROM emp;

   - 得出结果
   SELECT * FROM emp e,(SELECT DISTINCT mgr FROM emp) mgrtable WHERE e.empno = mgrtable.mgr;


-- where 接子查询
   -- 薪资高于10号部门平均工资的所有员工信息
   1. 10号部门平均工资
   SELECT AVG(sal) FROM emp WHERE deptno=10;
   2. 得出结果
   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
   1. 统计所有的部门的平均工资
   SELECT deptno, AVG(sal) FROM emp GROUP BY deptno;
   2. 30号部门的平均工资
   SELECT AVG(sal) FROM emp WHERE deptno=30;
   3.得出结果:
   SELECT deptno, AVG(sal) FROM emp GROUP BY deptno HAVING AVG(sal) > (SELECT AVG(sal) FROM emp WHERE deptno=30);

-- 列出达拉斯加工作的人中,比纽约平均工资高的人
1. 查处达拉斯加工作的人
1. 查询出达拉斯的部门编号
SELECT deptno FROM dept WHERE loc ='DALLAS';
2. SELECT * FROM emp WHERE deptno = ( SELECT deptno FROM dept WHERE loc ='DALLAS');

2. 查出纽约工作的人的平均工资
1. 查处纽约的部门编号
SELECT deptno FROM dept WHERE loc ='NEW YORK';
2. SELECT AVG(sal) FROM emp WHERE deptno = (SELECT deptno FROM dept WHERE loc ='NEW YORK');

3. 得出最终结果:
SELECT * FROM emp WHERE deptno = ( SELECT deptno FROM dept WHERE loc ='DALLAS')
AND
sal > (SELECT AVG(sal) FROM emp WHERE deptno = (SELECT deptno FROM dept WHERE loc ='NEW YORK'));

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