Mysql 子查询

-- 查询分类名称为手机数码的所有商品
1.查询分类名为手机数码的ID
SELECT cid FROM category WHERE cname='手机数码';
2.得出ID为1的结果
SELECT * FROM product WHERE cno = (SELECT cid FROM category WHERE cname='手机数码');
子查询练习:

• 子查询

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);
 
 
 
 
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');
 
 
 
 
 
 
 
```sql
-- 单行子查询(> < >= <= = <>)
    -- 查询出高于10号部门的平均工资的员工信息
 
-- 多行子查询(in  not in any all)
    -- 查询出比10号部门任何员工薪资高的员工信息
 
-- 多列子查询(实际使用较少)
    -- 和10号部门同名同工作的员工信息
 
-- select 后面接子查询    
    -- 获取员工的名字和部门的名字
    
-- from 后面接子查询
    -- 查询emp表中经理信息
    
-- where 后面接子查询 
    -- 薪资高于10号部门平均工资的所有员工信息
    
-- group by 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
 
    
-- 工资>JONES工资
-- 查询与SCOTT同一个部门的员工
-- 工资高于30号部门所有人的员工信息
-- 查询工作和工资与MARTIN完全相同的员工信息
-- 有两个以上直接下属的员工信息
-- 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
 

• 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
2. 列出达拉斯加工作的人中,比纽约平均工资高的人
3. 查询7369员工编号,姓名,经理编号和经理姓名
4. 查询出各个部门薪水最高的员工所有信息

面试题

CREATE TABLE test(
NAME CHAR(20),
kecheng CHAR(20),
fenshu CHAR(20)
);
 
INSERT INTO test VALUES('张三','语文',81),
('张三','数学',75),
('李四','语文',76),
('李四','数学',90),
('王五','语文',81),
('王五','数学',82);
 
--请用一条Sql语句查处分数大于80的学生

子查询练习及答案:

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'));
   ————————————————
   版权声明：本文为CSDN博主「mqingo」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。
   原文链接：https://blog.csdn.net/mqingo/article/details/84679590

原文链接：https://blog.csdn.net/mqingo/article/details/84679590