MYSQL子查詢練習
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');
--最高工資
SELECT MAX(sal) FROM emp;
--最少工資
SELECT MIN(sal) FROM emp;
--最高工資的員工資訊
SELECT * FROM emp WHERE sal = (SELECT MAX(sal) FROM emp);
--最低工資的員工資訊
SELECT * FROM emp WHERE sal = (SELECT MIN(sal) FROM emp);
-- 單行子查詢(> < >= <= = <>)
-- 查詢出高於10號部門的平均工資的員工資訊
1.10號部門的平均工資
SELECT AVG(sal) FROM emp WHERE deptno = 10;
2. 高於上面結果員工資訊
SELECT * FROM emp WHERE sal > (SELECT AVG(sal) FROM emp WHERE deptno = 10);
-- 多行子查詢(in not in any all) >any >all
-- 查詢出比10號部門任何員工薪資高的員工資訊
1. 查詢出10號部門最高工資
SELECT MAX(sal) FROM emp WHERE deptno = 10;
2. 得出結果
SELECT * FROM emp WHERE sal > (SELECT MAX(sal) FROM emp WHERE deptno = 10);
-- 查詢出比10號部門任意一個員工薪資高的所有員工資訊 : 只要比其中隨便一個工資都可以
SELECT sal FROM emp WHERE deptno = 10;
SELECT * FROM emp WHERE sal >ANY(SELECT sal FROM emp WHERE deptno = 10) AND deptno != 10;
-- 多列子查詢(實際使用較少) in
-- 和10號部門同名同工作的員工資訊
1. 查詢出10號部門所有人 名字和工作
SELECT ename,job FROM emp WHERE deptno=10;
2. 得出結果
SELECT * FROM emp WHERE (ename,job) IN (SELECT ename,job FROM emp WHERE deptno=10) AND deptno !=10;
-- Select後面接子查詢
-- 獲取員工的名字和部門的名字
SELECT ename,deptno FROM emp ;
SELECT ename,(SELECT dname FROM dept d WHERE d.deptno = e.deptno ) 部門名稱 FROM emp e ;
-- from後面接子查詢
-- 查詢emp表中所有管理層的資訊
SELECT DISTINCT mgr FROM emp;
- 得出結果
SELECT * FROM emp e,(SELECT DISTINCT mgr FROM emp) mgrtable WHERE e.empno = mgrtable.mgr;
-- where 接子查詢
-- 薪資高於10號部門平均工資的所有員工資訊
1. 10號部門平均工資
SELECT AVG(sal) FROM emp WHERE deptno=10;
2. 得出結果
SELECT * FROM emp WHERE sal > (SELECT AVG(sal) FROM emp WHERE deptno=10);
-- having後面接子查詢
-- 有哪些部門的平均工資高於30號部門的平均工資
1. 統計所有的部門的平均工資
SELECT deptno, AVG(sal) FROM emp GROUP BY deptno;
2. 30號部門的平均工資
SELECT AVG(sal) FROM emp WHERE deptno=30;
3.得出結果:
SELECT deptno, AVG(sal) FROM emp GROUP BY deptno HAVING AVG(sal) > (SELECT AVG(sal) FROM emp WHERE deptno=30);
-- 列出達拉斯加工作的人中,比紐約平均工資高的人
1. 查處達拉斯加工作的人
1. 查詢出達拉斯的部門編號
SELECT deptno FROM dept WHERE loc ='DALLAS';
2. SELECT * FROM emp WHERE deptno = ( SELECT deptno FROM dept WHERE loc ='DALLAS');
2. 查出紐約工作的人的平均工資
1. 查處紐約的部門編號
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. 得出最終結果:
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'));