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Mysql笔记整理2

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README.md
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# Bolg
> https://duyl328.github.io/
## 协议
本仓库采用双协议授权，即 MIT 协议和 CC-BY-4.0 协议：
- 所有`.md`文件采用 CC-BY-4.0 协议协议，你需要保留署名权
- 其他代码文件采用 MIT 协议，你可以自由使用
具体内容请查看[LICENSE](./LICENSE)文件。
docs/notes/MySql/17练习.md
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## 练习
基础：
​ 数据库的启停；
​ MySQL的登录（显示密码和不显示密码）；
​ 退出MySQL；
​ 查看数据库中有哪些库；
​ 使用数据库；
​ 创建数据库；
​ 查看数据库下有多少个表；
​ 查看表的结构，不显示表中数据；
​ 查看当前使用哪个数据库；
​ 删除数据库；
​ 如何结束一个sql语句（不使用’；‘）
​ 查看MySQL版本号；
​ 查看创建表时使用的语句；
​ sql数据导入；
​ 查看表中全部数据；
查询：
​ 简单查询；
​ 查询字段的简单的数学运算；
​ 给查询后的列重命名；
​ 给查询后的列使用中文名字命名；
​ AS关键字省略写法；
条件查询：
​ 语法；
​ 查询工资等于5000的员工姓名；
​ 查询SMITH工资；
​ 查询员工工资大于3000的员工；
​ 查询员工工资高于1100并低于3000的员工姓名及工资；（两种查询方式）
​ is null：
​ 找出哪些员工的福利（COMM）为NULL；
​ in ， not in：
​ 使用in找出工作是(MANAGER和SALESMAN）的员工；
\-------------------------------------------------------------------------------------------------
​ 模糊查询：
​ 查询名字中含有字母o的；
​ 查询名字中第二个字母是A的；
​ 查询名字中含有 ‘ _ ’的；
​ 查询名字最后一个字母是T的；
​ 排序：
​ 数据排序：
​ 找出岗位是salesman的员工，并按照工资降序排列；
​ 按照工资升序排，当工资相同时按照名字降序排；
函数：
​ 分组函数：
​ 找出最高、最低、平均、工资总和
​ 分组函数对NULL的处理；
​ 单行处理函数对NULL的处理；
​ 单行处理函数如何处理NULL；
​ count * 和count（字段名）的区别；
​ 找出工资高于平均工资的员工；
​ 找出每个岗位的最高薪资；
​ select、from、where、group by、having、order by的执行顺序；
​ 找出不同部门每个工作岗位的最高薪资；
​ 找出每个部门的最高薪资，要求显示大于2500的数据；（两种方式【where，having】）
​ 查询结果的去重；
连接查询:
​ 内连接：
​ 什么是笛卡尔积现象；
​ 笛卡尔积现象能避免吗；
​ 查询每个员工部门名称，要求显示员工名和部门名；
​ 找出每个员工的工资等级，要求显示员工名、工资、工资等级；
​ 找出每个员工对应的上级领导，要求显示员工名和领导名；
​ 外连接：
​ 找出每个员工的上级领导，没有也要显示（14条记录）
​ 找出哪个部门没有员工；
​ 为什么要为每个表取别名
​ 三表联查：
​ 找出每一个员工的部门名称以及工资等级
​ 找出每一个员工的部门名称以及工资等级，以及上级领导
## 1 - 5
#### 1、取得每个部门最高薪水的人员名称
第一步：取得每个部门最高薪水(按照部门编号分组，找出每一组最大值)
```sql
mysql> select deptno,max(sal) as maxsal from emp group by deptno;
+--------+---------+
| deptno | maxsal |
+--------+---------+
| 10 | 5000.00 |
| 20 | 3000.00 |
| 30 | 2850.00 |
+--------+---------+
```
第二步：将以上的查询结果当做一张临时表t，
t 和 emp 表连接，条件：t.deptno = e.deptno and t.maxsal = e.sal
```sql
select
e.ename, t.*
from
emp e
join
(select deptno,max(sal) as maxsal from emp group by deptno) t
on
t.deptno = e.deptno and t.maxsal = e.sal;
+-------+--------+---------+
| ename | deptno | maxsal |
+-------+--------+---------+
| BLAKE | 30 | 2850.00 |
| SCOTT | 20 | 3000.00 |
| KING | 10 | 5000.00 |
| FORD | 20 | 3000.00 |
+-------+--------+---------+
```
#### 2、哪些人的薪水在部门的平均薪水之上
第一步：找出每个部门的平均薪水
```sql
select deptno,avg(sal) as avgsal from emp group by deptno;
+--------+-------------+
| deptno | avgsal |
+--------+-------------+
| 10 | 2916.666667 |
| 20 | 2175.000000 |
| 30 | 1566.666667 |
+--------+-------------+
```
第二步：将以上查询结果当做t表，t和emp表连接
条件：部门编号相同，并且 emp 的 sal 大于 t 表的 avgsal
```sql
select
t.*, e.ename, e.sal
from
emp e
join
(select deptno,avg(sal) as avgsal from emp group by deptno) t
on
e.deptno = t.deptno and e.sal > t.avgsal;
+--------+-------------+-------+---------+
| deptno | avgsal | ename | sal |
+--------+-------------+-------+---------+
| 30 | 1566.666667 | ALLEN | 1600.00 |
| 20 | 2175.000000 | JONES | 2975.00 |
| 30 | 1566.666667 | BLAKE | 2850.00 |
| 20 | 2175.000000 | SCOTT | 3000.00 |
| 10 | 2916.666667 | KING | 5000.00 |
| 20 | 2175.000000 | FORD | 3000.00 |
+--------+-------------+-------+---------+
```
#### 3、取得部门中（所有人的）平均的薪水等级
平均的薪水等级：先计算每一个薪水的等级，然后找出薪水等级的平均值。
平均薪水的等级：先计算平均薪水，然后找出每个平均薪水的等级值。
第一步：找出每个人的薪水等级
emp e 和 salgrade s 表连接。
连接条件：e.sal between s.losal and s.hisal
```sql
select
e.ename,e.sal,e.deptno,s.grade
from
emp e
join
salgrade s
on
e.sal between s.losal and s.hisal;
+--------+---------+--------+-------+
| ename | sal | deptno | grade |
+--------+---------+--------+-------+
| CLARK | 2450.00 | 10 | 4 |
| KING | 5000.00 | 10 | 5 |
| MILLER | 1300.00 | 10 | 2 |
| SMITH | 800.00 | 20 | 1 |
| ADAMS | 1100.00 | 20 | 1 |
| SCOTT | 3000.00 | 20 | 4 |
| FORD | 3000.00 | 20 | 4 |
| JONES | 2975.00 | 20 | 4 |
| MARTIN | 1250.00 | 30 | 2 |
| TURNER | 1500.00 | 30 | 3 |
| BLAKE | 2850.00 | 30 | 4 |
| ALLEN | 1600.00 | 30 | 3 |
| JAMES | 950.00 | 30 | 1 |
| WARD | 1250.00 | 30 | 2 |
+--------+---------+--------+-------+
```
第二步：基于以上的结果继续按照deptno分组，求grade的平均值。
```sql
select
e.deptno,avg(s.grade)
from
emp e
join
salgrade s
on
e.sal between s.losal and s.hisal
group by
e.deptno;
+--------+--------------+
| deptno | avg(s.grade) |
+--------+--------------+
| 10 | 3.6667 |
| 20 | 2.8000 |
| 30 | 2.5000 |
+--------+--------------+
```
#### 4、不准用组函数（Max ），取得最高薪水
第一种：sal 降序，limit 1
```sql
select ename,sal from emp order by sal desc limit 1;
+-------+---------+
| ename | sal |
+-------+---------+
| KING | 5000.00 |
+-------+---------+
```
第二种方案：
```sql
select max(sal) from emp;
```
第三种方案：表的自连接
```sql
select sal from emp where sal not in(select distinct a.sal from emp a join emp b on a.sal < b.sal);
+---------+
| sal |
+---------+
| 5000.00 |
+---------+
```
```sql
select
distinct a.sal
from
emp a
join
emp b
on
a.sal < b.sal
```
a表
```sql
+---------+
| sal |
+---------+
| 800.00 |
| 1600.00 |
| 1250.00 |
| 2975.00 |
| 1250.00 |
| 2850.00 |
| 2450.00 |
| 3000.00 |
| 5000.00 |
| 1500.00 |
| 1100.00 |
| 950.00 |
| 3000.00 |
| 1300.00 |
+---------+
```
b表
```sql
+---------+
| sal |
+---------+
| 800.00 |
| 1600.00 |
| 1250.00 |
| 2975.00 |
| 1250.00 |
| 2850.00 |
| 2450.00 |
| 3000.00 |
| 5000.00 |
| 1500.00 |
| 1100.00 |
| 950.00 |
| 3000.00 |
| 1300.00 |
+---------+
```
#### 5、取得平均薪水最高的部门的部门编号
第一种方案：降序取第一个。
​ 第一步：找出每个部门的平均薪水
```sql
select deptno,avg(sal) as avgsal from emp group by deptno;
+--------+-------------+
| deptno | avgsal |
+--------+-------------+
| 10 | 2916.666667 |
| 20 | 2175.000000 |
| 30 | 1566.666667 |
+--------+-------------+
```
​ 第二步：降序选第一个。
```sql
select deptno,avg(sal) as avgsal from emp group by deptno order by avgsal desc limit 1;
+--------+-------------+
| deptno | avgsal |
+--------+-------------+
| 10 | 2916.666667 |
+--------+-------------+
```
第二种方案：max
​ 第一步：找出每个部门的平均薪水
```sql
select deptno,avg(sal) as avgsal from emp group by deptno;
+--------+-------------+
| deptno | avgsal |
+--------+-------------+
| 10 | 2916.666667 |
| 20 | 2175.000000 |
| 30 | 1566.666667 |
+--------+-------------+
```
​ 第二步：找出以上结果中avgsal最大的值。
```sql
select max(t.avgsal) from (select avg(sal) as avgsal from emp group by deptno) t;
+---------------+
| max(t.avgsal) |
+---------------+
| 2916.666667 |
+---------------+
```
​ 第三步：
```sql
select
deptno,avg(sal) as avgsal
from
emp
group by
deptno
having
avgsal = (select max(t.avgsal) from (select avg(sal) as avgsal from emp group by deptno) t);
+--------+-------------+
| deptno | avgsal |
+--------+-------------+
| 10 | 2916.666667 |
+--------+-------------+
```
## 5 - 10
#### 6、取得平均薪水最高的部门的部门名称
```sql
select
d.dname,avg(e.sal) as avgsal
from
emp e
join
dept d
on
e.deptno = d.deptno
group by
d.dname
order by
avgsal desc
limit
1;
+------------+-------------+
| dname | avgsal |
+------------+-------------+
| ACCOUNTING | 2916.666667 |
+------------+-------------+
```
#### 7、求平均薪水的等级最低的部门的部门名称
平均薪水是 800
平均薪水是 900
那么他俩都是 1 级别。
第一步：找出每个部门的平均薪水
```sql
select deptno,avg(sal) as avgsal from emp group by deptno;
+--------+-------------+
| deptno | avgsal |
+--------+-------------+
| 10 | 2916.666667 |
| 20 | 2175.000000 |
| 30 | 1566.666667 |
+--------+-------------+
```
第二步：找出每个部门的平均薪水的等级
以上 t 表和 salgrade 表连接，条件：t.avgsal between s.losal and s.hisal
```sql
select
t.*,s.grade
from
(select d.dname,avg(sal) as avgsal from emp e join dept d on e.deptno = d.deptno group by d.dname) t
join
salgrade s
on
t.avgsal between s.losal and s.hisal;
+------------+-------------+-------+
| dname | avgsal | grade |
+------------+-------------+-------+
| SALES | 1566.666667 | 3 |
| ACCOUNTING | 2916.666667 | 4 |
| RESEARCH | 2175.000000 | 4 |
+------------+-------------+-------+
```
```sql
select
t.*,s.grade
from
(select d.dname,avg(sal) as avgsal from emp e join dept d on e.deptno = d.deptno group by d.dname) t
join
salgrade s
on
t.avgsal between s.losal and s.hisal
where
s.grade = (select grade from salgrade where (select avg(sal) as avgsal from emp group by deptno order by avgsal asc limit 1) between losal and hisal);
+-------+-------------+-------+
| dname | avgsal | grade |
+-------+-------------+-------+
| SALES | 1566.666667 | 3 |
+-------+-------------+-------+
```
抛开之前的，最低等级你怎么着？
平均薪水最低的对应的等级一定是最低的.
```sql
select avg(sal) as avgsal from emp group by deptno order by avgsal asc limit 1;
+-------------+
| avgsal |
+-------------+
| 1566.666667 |
+-------------+
```
```sql
select grade from salgrade where (select avg(sal) as avgsal from emp group by deptno order by avgsal asc limit 1) between losal and hisal;
+-------+
| grade |
+-------+
| 3 |
+-------+
```
#### 8、取得比普通员工(员工代码没有在 mgr 字段上出现的) 的最高薪水还要高的领导人姓名
> 比“普通员工的最高薪水”还要高的一定是领导！
> 没毛病！！！！
```sql
mysql> select distinct mgr from emp where mgr is not null;
+------+
| mgr |
+------+
| 7902 |
| 7698 |
| 7839 |
| 7566 |
| 7788 |
| 7782 |
+------+
```
员工编号没有在以上范围内的都是普通员工。
第一步：找出普通员工的最高薪水！
not in 在使用的时候，后面小括号中记得排除NULL。
```sql
select max(sal) from emp where empno not in(select distinct mgr from emp where mgr is not null);
+----------+
| max(sal) |
+----------+
| 1600.00 |
+----------+
```
第二步：找出高于1600的
```sql
select ename,sal from emp where sal > (select max(sal) from emp where empno not in(select distinct mgr from emp where mgr is not null));
+-------+---------+
| ename | sal |
+-------+---------+
| JONES | 2975.00 |
| BLAKE | 2850.00 |
| CLARK | 2450.00 |
| SCOTT | 3000.00 |
| KING | 5000.00 |
| FORD | 3000.00 |
+-------+---------+
```
#### 9、取得薪水最高的前五名员工
```sql
select ename,sal from emp order by sal desc limit 5;
+-------+---------+
| ename | sal |
+-------+---------+
| KING | 5000.00 |
| SCOTT | 3000.00 |
| FORD | 3000.00 |
| JONES | 2975.00 |
| BLAKE | 2850.00 |
+-------+---------+
```
#### 10、取得薪水最高的第六到第十名员工
```sql
select ename,sal from emp order by sal desc limit 5;
+-------+---------+
| ename | sal |
+-------+---------+
| KING | 5000.00 |
| SCOTT | 3000.00 |
| FORD | 3000.00 |
| JONES | 2975.00 |
| BLAKE | 2850.00 |
+-------+---------+
select ename,sal from emp order by sal desc limit 5, 5;
+--------+---------+
| ename | sal |
+--------+---------+
| CLARK | 2450.00 |
| ALLEN | 1600.00 |
| TURNER | 1500.00 |
| MILLER | 1300.00 |
| MARTIN | 1250.00 |
+--------+---------+
```
## 11 - 15
#### 11、取得最后入职的 5 名员工
日期也可以降序，升序。
```sql
select ename,hiredate from emp order by hiredate desc limit 5;
+--------+------------+
| ename | hiredate |
+--------+------------+
| ADAMS | 1987-05-23 |
| SCOTT | 1987-04-19 |
| MILLER | 1982-01-23 |
| FORD | 1981-12-03 |
| JAMES | 1981-12-03 |
+--------+------------+
```
#### 12、取得每个薪水等级有多少员工
分组 count
第一步：找出每个员工的薪水等级
```sql
select
e.ename,e.sal,s.grade
from
emp e
join
salgrade s
on
e.sal between s.losal and s.hisal;
+--------+---------+-------+
| ename | sal | grade |
+--------+---------+-------+
| SMITH | 800.00 | 1 |
| ALLEN | 1600.00 | 3 |
| WARD | 1250.00 | 2 |
| JONES | 2975.00 | 4 |
| MARTIN | 1250.00 | 2 |
| BLAKE | 2850.00 | 4 |
| CLARK | 2450.00 | 4 |
| SCOTT | 3000.00 | 4 |
| KING | 5000.00 | 5 |
| TURNER | 1500.00 | 3 |
| ADAMS | 1100.00 | 1 |
| JAMES | 950.00 | 1 |
| FORD | 3000.00 | 4 |
| MILLER | 1300.00 | 2 |
+--------+---------+-------+
```
第二步：继续按照grade分组统计数量
```sql
select
s.grade ,count(*)
from
emp e
join
salgrade s
on
e.sal between s.losal and s.hisal
group by
s.grade;
+-------+----------+
| grade | count(*) |
+-------+----------+
| 1 | 3 |
| 2 | 3 |
| 3 | 2 |
| 4 | 5 |
| 5 | 1 |
+-------+----------+
```
#### 13、面试题：
有 3 个表 S(学生表)，C（课程表），SC（学生选课表）
S（SNO，SNAME）代表（学号，姓名）
C（CNO，CNAME，CTEACHER）代表（课号，课名，教师）
SC（SNO，CNO，SCGRADE）代表（学号，课号，成绩）
问题：
1，找出没选过“黎明”老师的所有学生姓名。
2，列出 2 门以上（含2 门）不及格学生姓名及平均成绩。
3，即学过 1 号课程又学过 2 号课所有学生的姓名。
#### 14、列出所有员工及领导的姓名
```sql
select
a.ename '员工', b.ename '领导'
from
emp a
left join
emp b
on
a.mgr = b.empno;
+--------+-------+
| 员工 | 领导 |
+--------+-------+
| SMITH | FORD |
| ALLEN | BLAKE |
| WARD | BLAKE |
| JONES | KING |
| MARTIN | BLAKE |
| BLAKE | KING |
| CLARK | KING |
| SCOTT | JONES |
| KING | NULL |
| TURNER | BLAKE |
| ADAMS | SCOTT |
| JAMES | BLAKE |
| FORD | JONES |
| MILLER | CLARK |
+--------+-------+
```
#### 15、列出受雇日期早于其直接上级的所有员工的编号,姓名,部门名称
```sql
emp a 员工表
emp b 领导表
a.mgr = b.empno and a.hiredate < b.hiredate
select
a.ename '员工', a.hiredate, b.ename '领导', b.hiredate, d.dname
from
emp a
join
emp b
on
a.mgr = b.empno
join
dept d
on
a.deptno = d.deptno
where
a.hiredate < b.hiredate;
+-------+------------+-------+------------+------------+
| 员工 | hiredate | 领导 | hiredate | dname |
+-------+------------+-------+------------+------------+
| CLARK | 1981-06-09 | KING | 1981-11-17 | ACCOUNTING |
| SMITH | 1980-12-17 | FORD | 1981-12-03 | RESEARCH |
| JONES | 1981-04-02 | KING | 1981-11-17 | RESEARCH |
| ALLEN | 1981-02-20 | BLAKE | 1981-05-01 | SALES |
| WARD | 1981-02-22 | BLAKE | 1981-05-01 | SALES |
| BLAKE | 1981-05-01 | KING | 1981-11-17 | SALES |
+-------+------------+-------+------------+------------+
```
## 16 - 20
#### 16、 列出部门名称和这些部门的员工信息, 同时列出那些没有员工的部门
```sql
select
e.*,d.dname
from
emp e
right join
dept d
on
e.deptno = d.deptno;
+-------+--------+-----------+------+------------+---------+---------+--------+------------+
| EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO | dname |
+-------+--------+-----------+------+------------+---------+---------+--------+------------+
| 7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450.00 | NULL | 10 | ACCOUNTING |
| 7839 | KING | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL | 10 | ACCOUNTING |
| 7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300.00 | NULL | 10 | ACCOUNTING |
| 7369 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | NULL | 20 | RESEARCH |
| 7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | NULL | 20 | RESEARCH |
| 7788 | SCOTT | ANALYST | 7566 | 1987-04-19 | 3000.00 | NULL | 20 | RESEARCH |
| 7876 | ADAMS | CLERK | 7788 | 1987-05-23 | 1100.00 | NULL | 20 | RESEARCH |
| 7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000.00 | NULL | 20 | RESEARCH |
| 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600.00 | 300.00 | 30 | SALES |
| 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 | SALES |
| 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 | 30 | SALES |
| 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850.00 | NULL | 30 | SALES |
| 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 | 0.00 | 30 | SALES |
| 7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950.00 | NULL | 30 | SALES |
| NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | OPERATIONS |
+-------+--------+-----------+------+------------+---------+---------+--------+------------+
```
#### 17、列出至少有 5 个员工的所有部门
按照部门编号分组，计数，筛选出 >= 5
```sql
select
deptno
from
emp
group by
deptno
having
count(*) >= 5;
+--------+
| deptno |
+--------+
| 20 |
| 30 |
+--------+
```
#### 18、列出薪金比"SMITH" 多的所有员工信息
```sql
select ename,sal from emp where sal > (select sal from emp where ename = 'SMITH');
+--------+---------+
| ename | sal |
+--------+---------+
| ALLEN | 1600.00 |
| WARD | 1250.00 |
| JONES | 2975.00 |
| MARTIN | 1250.00 |
| BLAKE | 2850.00 |
| CLARK | 2450.00 |
| SCOTT | 3000.00 |
| KING | 5000.00 |
| TURNER | 1500.00 |
| ADAMS | 1100.00 |
| JAMES | 950.00 |
| FORD | 3000.00 |
| MILLER | 1300.00 |
+--------+---------+
```
#### 19、 列出所有"CLERK"( 办事员) 的姓名及其部门名称, 部门的人数
```sql
select ename,job from emp where job = 'CLERK';
+--------+-------+
| ename | job |
+--------+-------+
| SMITH | CLERK |
| ADAMS | CLERK |
| JAMES | CLERK |
| MILLER | CLERK |
+--------+-------+
select
e.ename,e.job,d.dname
from
emp e
join
dept d
on
e.deptno = d.deptno
where
e.job = 'CLERK';
+--------+-------+------------+
| ename | job | dname |
+--------+-------+------------+
| MILLER | CLERK | ACCOUNTING |
| SMITH | CLERK | RESEARCH |
| ADAMS | CLERK | RESEARCH |
| JAMES | CLERK | SALES |
+--------+-------+------------+
select
e.ename,e.job,d.dname,d.deptno
from
emp e
join
dept d
on
e.deptno = d.deptno
where
e.job = 'CLERK';
+--------+-------+------------+--------+
| ename | job | dname | deptno |
+--------+-------+------------+--------+
| MILLER | CLERK | ACCOUNTING | 10 |
| SMITH | CLERK | RESEARCH | 20 |
| ADAMS | CLERK | RESEARCH | 20 |
| JAMES | CLERK | SALES | 30 |
+--------+-------+------------+--------+
//每个部门的人数？
select deptno, count(*) as deptcount from emp group by deptno;
+--------+-----------+
| deptno | deptcount |
+--------+-----------+
| 10 | 3 |
| 20 | 5 |
| 30 | 6 |
+--------+-----------+
select
t1.*,t2.deptcount
from
(select
e.ename,e.job,d.dname,d.deptno
from
emp e
join
dept d
on
e.deptno = d.deptno
where
e.job = 'CLERK') t1
join
(select deptno, count(*) as deptcount from emp group by deptno) t2
on
t1.deptno = t2.deptno;
+--------+-------+------------+--------+-----------+
| ename | job | dname | deptno | deptcount |
+--------+-------+------------+--------+-----------+
| MILLER | CLERK | ACCOUNTING | 10 | 3 |
| SMITH | CLERK | RESEARCH | 20 | 5 |
| ADAMS | CLERK | RESEARCH | 20 | 5 |
| JAMES | CLERK | SALES | 30 | 6 |
+--------+-------+------------+--------+-----------+
```
#### 20、列出最低薪金大于 1500 的各种工作及从事此工作的全部雇员人数
按照工作岗位分组求最小值。
```sql
select job,count(*) from emp group by job having min(sal) > 1500;
+-----------+----------+
| job | count(*) |
+-----------+----------+
| ANALYST | 2 |
| MANAGER | 3 |
| PRESIDENT | 1 |
+-----------+----------+
```
## 21 - 25
#### 21、列出在部门"SALES"< 销售部> 工作的员工的姓名, 假定不知道销售部的部门编号.
```sql
select ename from emp where deptno = (select deptno from dept where dname = 'SALES');
+--------+
| ename |
+--------+
| ALLEN |
| WARD |
| MARTIN |
| BLAKE |
| TURNER |
| JAMES |
+--------+
```
#### 22、列出薪金高于公司平均薪金的所有员工, 所在部门, 上级领导, 雇员的工资等级.
```sql
select
e.ename '员工',d.dname,l.ename '领导',s.grade
from
emp e
join
dept d
on
e.deptno = d.deptno
left join
emp l
on
e.mgr = l.empno
join
salgrade s
on
e.sal between s.losal and s.hisal
where
e.sal > (select avg(sal) from emp);
+-------+------------+-------+-------+
| 员工 | dname | 领导 | grade |
+-------+------------+-------+-------+
| JONES | RESEARCH | KING | 4 |
| BLAKE | SALES | KING | 4 |
| CLARK | ACCOUNTING | KING | 4 |
| SCOTT | RESEARCH | JONES | 4 |
| KING | ACCOUNTING | NULL | 5 |
| FORD | RESEARCH | JONES | 4 |
+-------+------------+-------+-------+
```
#### 23、 列出与"SCOTT" 从事相同工作的所有员工及部门名称
```sql
select job from emp where ename = 'SCOTT';
+---------+
| job |
+---------+
| ANALYST |
+---------+
select
e.ename,e.job,d.dname
from
emp e
join
dept d
on
e.deptno = d.deptno
where
e.job = (select job from emp where ename = 'SCOTT')
and
e.ename <> 'SCOTT';
+-------+---------+----------+
| ename | job | dname |
+-------+---------+----------+
| FORD | ANALYST | RESEARCH |
+-------+---------+----------+
```
#### 24、列出薪金等于部门 30 中员工的薪金的其他员工的姓名和薪金.
```sql
select distinct sal from emp where deptno = 30;
+---------+
| sal |
+---------+
| 1600.00 |
| 1250.00 |
| 2850.00 |
| 1500.00 |
| 950.00 |
+---------+
select
ename,sal
from
emp
where
sal in(select distinct sal from emp where deptno = 30)
and
deptno <> 30;
Empty set (0.00 sec)
```
#### 25、列出薪金高于在部门 30 工作的所有员工的薪金的员工姓名和薪金. 部门名称
```sql
select max(sal) from emp where deptno = 30;
+----------+
| max(sal) |
+----------+
| 2850.00 |
+----------+
select
e.ename,e.sal,d.dname
from
emp e
join
dept d
on
e.deptno = d.deptno
where
e.sal > (select max(sal) from emp where deptno = 30);
+-------+---------+------------+
| ename | sal | dname |
+-------+---------+------------+
| KING | 5000.00 | ACCOUNTING |
| JONES | 2975.00 | RESEARCH |
| SCOTT | 3000.00 | RESEARCH |
| FORD | 3000.00 | RESEARCH |
+-------+---------+------------+
```
#### 26 - 30
#### 26、列出在每个部门工作的员工数量, 平均工资和平均服务期限
没有员工的部门，部门人数是 0
```sql
select
d.deptno, count(e.ename) ecount,ifnull(avg(e.sal),0) as avgsal, if null(avg(timestampdiff(YEAR, hiredate, now())), 0) as avgservicetime
from
emp e
right join
dept d
on
e.deptno = d.deptno
group by
d.deptno;
+--------+--------+-------------+----------------+
| deptno | ecount | avgsal | avgservicetime |
+--------+--------+-------------+----------------+
| 10 | 3 | 2916.666667 | 38.0000 |
| 20 | 5 | 2175.000000 | 35.8000 |
| 30 | 6 | 1566.666667 | 38.3333 |
| 40 | 0 | 0.000000 | 0.0000 |
+--------+--------+-------------+----------------+
```
在 mysql 当中怎么计算两个日期的“年差”，差了多少年？
TimeStampDiff (间隔类型, 前一个日期, 后一个日期)
```sql
timestampdiff(YEAR, hiredate, now())
间隔类型：
SECOND 秒，
MINUTE 分钟，
HOUR 小时，
DAY 天，
WEEK 星期
MONTH 月，
QUARTER 季度，
YEAR 年
```
#### 27、 列出所有员工的姓名、部门名称和工资。
```sql
select
e.ename,d.dname,e.sal
from
emp e
join
dept d
on
e.deptno = d.deptno;
+--------+------------+---------+
| ename | dname | sal |
+--------+------------+---------+
| CLARK | ACCOUNTING | 2450.00 |
| KING | ACCOUNTING | 5000.00 |
| MILLER | ACCOUNTING | 1300.00 |
| SMITH | RESEARCH | 800.00 |
| JONES | RESEARCH | 2975.00 |
| SCOTT | RESEARCH | 3000.00 |
| ADAMS | RESEARCH | 1100.00 |
| FORD | RESEARCH | 3000.00 |
| ALLEN | SALES | 1600.00 |
| WARD | SALES | 1250.00 |
| MARTIN | SALES | 1250.00 |
| BLAKE | SALES | 2850.00 |
| TURNER | SALES | 1500.00 |
| JAMES | SALES | 950.00 |
+--------+------------+---------+
```
#### 28、列出所有部门的详细信息和人数
```sql
select
d.deptno,d.dname,d.loc,count(e.ename)
from
emp e
right join
dept d
on
e.deptno = d.deptno
group by
d.deptno,d.dname,d.loc;
+--------+------------+----------+----------------+
| deptno | dname | loc | count(e.ename) |
+--------+------------+----------+----------------+
| 10 | ACCOUNTING | NEW YORK | 3 |
| 20 | RESEARCH | DALLAS | 5 |
| 30 | SALES | CHICAGO | 6 |
| 40 | OPERATIONS | BOSTON | 0 |
+--------+------------+----------+----------------+
```
#### 29、列出各种工作的最低工资及从事此工作的雇员姓名
```sql
select
job,min(sal) as minsal
from
emp
group by
job;
+-----------+----------+
| job | minsal |
+-----------+----------+
| ANALYST | 3000.00 |
| CLERK | 800.00 |
| MANAGER | 2450.00 |
| PRESIDENT | 5000.00 |
| SALESMAN | 1250.00 |
+-----------+----------+
emp e 和以上 t 连接
select
e.ename,t.*
from
emp e
join
(select
job,min(sal) as minsal
from
emp
group by
job) t
on
e.job = t.job and e.sal = t.minsal;
+--------+-----------+---------+
| ename | job | minsal |
+--------+-----------+---------+
| SMITH | CLERK | 800.00 |
| WARD | SALESMAN | 1250.00 |
| MARTIN | SALESMAN | 1250.00 |
| CLARK | MANAGER | 2450.00 |
| SCOTT | ANALYST | 3000.00 |
| KING | PRESIDENT | 5000.00 |
| FORD | ANALYST | 3000.00 |
+--------+-----------+---------+
```
#### 30、列出各个部门的 MANAGER( 领导) 的最低薪金
```sql
select
deptno, min(sal)
from
emp
where
job = 'MANAGER'
group by
deptno;
+--------+----------+
| deptno | min(sal) |
+--------+----------+
| 10 | 2450.00 |
| 20 | 2975.00 |
| 30 | 2850.00 |
+--------+----------+
```
## 30 - 34
#### 31、列出所有员工的 年工资, 按 年薪从低到高排序
```sql
select
ename,(sal + ifnull(comm,0)) * 12 as yearsal
from
emp
order by
yearsal asc;
+--------+----------+
| ename | yearsal |
+--------+----------+
| SMITH | 9600.00 |
| JAMES | 11400.00 |
| ADAMS | 13200.00 |
| MILLER | 15600.00 |
| TURNER | 18000.00 |
| WARD | 21000.00 |
| ALLEN | 22800.00 |
| CLARK | 29400.00 |
| MARTIN | 31800.00 |
| BLAKE | 34200.00 |
| JONES | 35700.00 |
| FORD | 36000.00 |
| SCOTT | 36000.00 |
| KING | 60000.00 |
+--------+----------+
```
#### 32、求出员工领导的薪水超过3000的员工名称与领导
```sql
select
a.ename '员工',b.ename '领导'
from
emp a
join
emp b
on
a.mgr = b.empno
where
b.sal > 3000;
+-------+------+
| 员工 | 领导 |
+-------+------+
| JONES | KING |
| BLAKE | KING |
| CLARK | KING |
+-------+------+
```
#### 33、求出部门名称中, 带'S'字符的部门员工的工资合计、部门人数
```sql
select
d.deptno,d.dname,d.loc,count(e.ename),ifnull(sum(e.sal),0) as sumsal
from
emp e
right join
dept d
on
e.deptno = d.deptno
where
d.dname like '%S%'
group by
d.deptno,d.dname,d.loc;
+--------+------------+---------+----------------+----------+
| deptno | dname | loc | count(e.ename) | sumsal |
+--------+------------+---------+----------------+----------+
| 20 | RESEARCH | DALLAS | 5 | 10875.00 |
| 30 | SALES | CHICAGO | 6 | 9400.00 |
| 40 | OPERATIONS | BOSTON | 0 | 0.00 |
+--------+------------+---------+----------------+----------+
```
#### 34、给任职日期超过 30 年的员工加薪 10%.
```sql
update emp set sal = sal * 1.1 where timestampdiff(YEAR, hiredate, now()) > 30;
```