（傲娇的白狐）MYsql查询语句练习

- 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
) ;

select * from emp;

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(> < >= <= = <>)
-- 查询出高于10号部门的平均工资的员工信息

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

select AVG(e.sal) from dept d,emp e where d.deptno=e.deptno and d.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)

-- 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 e1
where exists(select *
from emp e2
where e2.ename=e1.ename and e2.deptno=e1.deptno and e2.deptno=10) and e1.deptno<>10;

-- select 后面接子查询
-- 获取员工的名字和部门的名字

select ename,dname from dept t ,emp e WHERE
t.deptno=e.deptno

-- from 后面接子查询
-- 查询emp表中经理信息

select * from dept t ,emp e WHERE
t.deptno=e.deptno and t.dname='RESEARCH'

-- 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

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>(
select max(sal) from emp where deptno=30
};
select *
from emp
where sal>(select max(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 e1
where exists(select *
from emp e2
where e1.job=e2.job and e1.sal=e2.sal and e2.ename='MARTIN') and ename<>'MARTIN';

--另一种写法（多列子查询）
SELECT *
FROM emp
WHERE (job,sal) IN (SELECT job,sal
FROM emp
WHERE ename='MARTIN') and ename<>'MARTIN';
-- 有两个以上直接下属的员工信息

select *
from emp e1
where (select count(*)
from emp e2
where e2.mgr=e1.empno)>2;

--另一种方法
SELECT * FROM emp e1
WHERE e1.empno IN (SELECT e2.mgr
FROM emp e2
GROUP BY e2.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 ename,sal,dname,loc
from emp inner join dept on empno=7788 and emp.deptno=dept.deptno;

 

- 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 sal>(
select avg(sal) from emp e2 where e2.deptno=e1.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 INNER JOIN dept on emp.deptno=dept.deptno
and sal>(

select avg(sal) from emp INNER JOIN dept on emp.deptno=dept.deptno
and loc='NEW YORK')
and loc='DALLAS'

3. 查询7369员工编号,姓名,经理编号和经理姓名

select e1.ename,e1.empno,e1.mgr 经理编号,e2.ename 经理姓名
from emp e1 INNER JOIN emp e2 on e1.mgr =e2.empno

4. 查询出各个部门薪水最高的员工所有信息
select * from emp e1
where sal=(
select MAX(sal) from emp e2 where e2.deptno=e1.deptno
)
select *
from emp e1
where sal=(select max(sal)
from emp e2
where e2.deptno=e1.deptno);
#### 面试题

```sql
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 name from (
-- 根据名字分组 获得 几门课程 总分数 和姓名
select count(*) t, sum(fenshu) num, name from test group by name
)
--查出来的定义为 s s的总成绩如果大于 几门课*80总成绩的话 就显示
as s where s.num>80*t;