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0基础SQL练习之(子查询)【不会敲的有答案呦

- 子查询

创建sql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);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');

-- 单行子查询(> = <= = )

select * from emp where sal >(select avg(sal) from emp where deptno=10) is not null;

    -- 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) and deptno !=10 

-- 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

select * from emp where sal>(select max(sal) from emp where deptno=10) and deptno !=10 

-- 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 * from emp where(ename,job) in(select ename,job from emp where deptno=10);

-- select 后面接子查询    
    -- 获取员工的名字和部门的名字

select * from emp WHERE emp.name in (select ename,job from emp);

-- from 后面接子查询
    -- 查询emp表中经理信息

 

SELECT * from emp where job='MANAGER'

-- 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

 

select * from emp where sal >(select avg(sal) from emp where deptno=10);    

    
-- 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
    #查找30号部门的平均工资

  

  select avg(sal) from  emp where deptno=30;    select deptno,avg(sal) from emp GROUP BY deptno HAVING avg(sal)>(select avg(sal) from  emp where deptno=30);    SELECT deptno, AVG(sal) FROM emp GROUP BY deptno HAVING AVG(sal) > (SELECT AVG(sal) FROM emp WHERE deptno=30);    

    -- 工资>JONES工资
-- 查询与SCOTT同一个部门的员工

 

select * from emp where ename="SCOTT";select ename from emp where emp in (select * from emp where ename="SCOTT");#select * from 员工表 where 部门 in (select 部门 from 员工表 where 姓名='张三') and 姓名'张三'select * from emp where deptno in(select deptno from emp where ename="SCOTT")and ename"SCOTT";select * from emp;select * from dept;

-- 工资高于30号部门所有人的员工信息

select sal from emp where deptno=30;select * from emp where sal>all(select sal from emp where deptno=30) and deptno!=30;

-- 查询工作和工资与MARTIN完全相同的员工信息
#先查出MARTIN的工作和工资与

 

select job,mgr from emp where ename="MARTIN";

#完全相同的员工信息 (job,sal)表示一个集合; in (集合) 包含 

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 where mgr in(select mgr from emp GROUP BY mgr HAVING count(mgr)>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,dept d where e.deptno=d.deptno and e.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 e1 where e1.sal> (select avg(e2.sal) from emp e2 where e1.deptno=e2.deptno GROUP BY e2.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=(select deptno from dept where loc="DALLAS") and sal>(select avg(sal) from emp where deptno=(select deptno from dept where loc="NEW YORK"))

#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.deptno,d.dname from emp e,dept d where d.deptno=e.deptno and e.empno=7369;

#4. 查询出各个部门薪水最高的员工所有信息

select * from emp e where e.sal=(select max(sal) from emp ep where e.deptno=ep.deptno GROUP BY deptno);    select * from  dept;    select * from  emp

到最后一个是面试题啦
#### 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

SELECT *from test WHERE fenshu > 80