MySQL作业题

一、取得每个部门最高薪水的人员名称

第一步：取得每个部门的最高薪水
select e.deptno, max(e.sal) as 'maxSal' from emp e group by e.deptno;
+--------+---------+
| deptno | maxSal  |
+--------+---------+
|     20 | 3000.00 |
|     30 | 2850.00 |
|     10 | 5000.00 |
+--------+---------+
3 rows in set (0.00 sec)

第二步：将以上结果当做临时表t，t表和emp e表进行连接，条件是：t.deptno = e.deptno and t.maxSal = e.sal

select 
	e.ename, e.sal, d.dname, d.deptno
from
	emp e
inner join 
	(select e.deptno, max(e.sal) as 'maxSal' from emp e group by e.deptno) t
on
	(e.sal = t.maxSal) and (e.deptno = t.deptno)
inner join
	dept d
on
	e.deptno = d.deptno
order by
	e.sal asc;


解法二：
select 
	e.ename, e.sal, d.dname, d.deptno
from
	emp e
inner join
	dept d
on
	e.deptno = d.deptno
where 
	e.sal in (select max(e.sal) as 'maxSal' from emp e group by e.deptno)
order by
	e.sal asc;

+-------+---------+------------+--------+
| ename | sal     | dname      | deptno |
+-------+---------+------------+--------+
| BLAKE | 2850.00 | SALES      |     30 |
| SCOTT | 3000.00 | RESEARCH   |     20 |
| FORD  | 3000.00 | RESEARCH   |     20 |
| KING  | 5000.00 | ACCOUNTING |     10 |
+-------+---------+------------+--------+
4 rows in set (0.00 sec)

二、那些人的薪水在部门平均薪水之上

第一步：找出每个部门的平均薪水
select e.deptno, avg(e.sal) as 'avgSal' from emp e group by e.deptno;
+--------+-------------+
| deptno | avgSal      |
+--------+-------------+
|     20 | 2175.000000 |
|     30 | 1566.666667 |
|     10 | 2916.666667 |
+--------+-------------+

第二步：将以上查询的结果当做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
select 
	e.ename as '员工名', e.sal as '员工薪资', d.dname as '部门名称', d.deptno as '部门编号', t.avgSal as '部门平均薪资'
from
	emp e
inner join 
	(select e.deptno, avg(e.sal) as 'avgSal' from emp e group by e.deptno) as t
on
	e.deptno = t.deptno
inner join
	dept d
on
	e.deptno = d.deptno
where
	e.sal > t.avgSal
order by
	d.dname asc;

+--------+----------+------------+----------+--------------+
| 员工名 | 员工薪资 | 部门名称   | 部门编号 | 部门平均薪资 |
+--------+----------+------------+----------+--------------+
| KING   |  5000.00 | ACCOUNTING |       10 |  2916.666667 |
| JONES  |  2975.00 | RESEARCH   |       20 |  2175.000000 |
| SCOTT  |  3000.00 | RESEARCH   |       20 |  2175.000000 |
| FORD   |  3000.00 | RESEARCH   |       20 |  2175.000000 |
| ALLEN  |  1600.00 | SALES      |       30 |  1566.666667 |
| BLAKE  |  2850.00 | SALES      |       30 |  1566.666667 |
+--------+----------+------------+----------+--------------+
6 rows in set (0.00 sec)

三、取得部门中（所有人的）平均的薪水等级

select 
	d.deptno as '部门编号', max(d.dname) as '部门名称', avg(s.grade) as '平均的薪资等级'
from
	emp e
inner join 
	salgrade s
on
	e.sal between s.losal and s.hisal
inner join
	dept d
on
	e.deptno = d.deptno
group by
	e.deptno
order by
	d.deptno asc;

+----------+------------+----------------+
| 部门编号 | 部门名称   | 平均的薪资等级 |
+----------+------------+----------------+
|       10 | ACCOUNTING |         3.6667 |
|       20 | RESEARCH   |         2.8000 |
|       30 | SALES      |         2.5000 |
+----------+------------+----------------+
3 rows in set (0.01 sec)

四、不准用组函数（max），取得最高薪水（给出两种解决方案）

第一种方法：
select 
    e.ename, e.sal 
from 
    emp e 
order by 
    e.sal desc 
limit 
    1;

+-------+---------+
| ename | sal     |
+-------+---------+
| KING  | 5000.00 |
+-------+---------+
1 row in set (0.00 sec)


第二种方法：表的自连接

第一步：只会筛选出除最大值以外的所有数据
select distinct a.sal from emp a inner join emp b on a.sal < b.sal;
+---------+
| sal     |
+---------+
|  800.00 |
|  950.00 |
| 1100.00 |
| 1250.00 |
| 1300.00 |
| 1500.00 |
| 1600.00 |
| 2450.00 |
| 2850.00 |
| 2975.00 |
| 3000.00 |
+---------+
11 rows in set (0.00 sec)

第二步：采取子查询语法
select 
    e.ename, e.sal
from
    emp e
where 
    e.sal not in (select distinct a.sal from emp a inner join emp b on a.sal < b.sal);

+-------+---------+
| ename | sal     |
+-------+---------+
| KING  | 5000.00 |
+-------+---------+
1 row in set (0.00 sec)

五、取得平均薪水最高的部门的部门编号及部门名称

第一种方案：使用limit取第一个

第一步：找出每个部门的平均薪水
select 
    e.deptno, avg(e.sal) as 'avgSal'
from
    emp e
group by
    e.deptno;
+--------+-------------+
| deptno | avgSal      |
+--------+-------------+
|     20 | 2175.000000 |
|     30 | 1566.666667 |
|     10 | 2916.666667 |
+--------+-------------+
3 rows in set (0.00 sec)

第二步：降序选第一个
select 
	d.deptno as '部门编号', max(d.dname) as '部门名称', avg(e.sal) as '平均薪资'
from 
	emp e 
inner join
	dept d
on
	e.deptno = d.deptno
group by 
	e.deptno
order by
	平均薪资 desc
limit
	1;
+----------+------------+-------------+
| 部门编号 | 部门名称   | 平均薪资    |
+----------+------------+-------------+
|       10 | ACCOUNTING | 2916.666667 |
+----------+------------+-------------+
1 row in set (0.00 sec)

第二种方案：使用max取最大值

第一步：找出每个部门中平均薪水的最大值
select max(t.avgSal) from (select avg(e.sal) as 'avgSal' from emp e group by e.deptno) as t;
+---------------+
| max(t.avgSal) |
+---------------+
|   2916.666667 |
+---------------+

select 
    e.deptno as '部门编号', max(d.dname) as '部门名称', avg(e.sal) as '平均薪资'
from
    emp e
inner join
    dept d
on
    e.deptno = d.deptno
group by
    e.deptno
having
    avg(e.sal) = (select max(t.avgSal) from (select avg(e.sal) as 'avgSal' from emp e group by e.deptno) as t);
+----------+------------+-------------+
| 部门编号 | 部门名称   | 平均薪资    |
+----------+------------+-------------+
|       10 | ACCOUNTING | 2916.666667 |
+----------+------------+-------------+

六、求平均薪水的等级最低的部门的部门名称

平均薪水是最低的，则等级一定是最低的

平均薪水不是最低的，也有可能等级是最低的，因为薪水等级的范围是一个区间

也就是说，平均薪水的等级最低的部门有可能有多个

平均薪水是800

平均薪水是900

则这两个都是1级别

第一步：找出每个部门的平均薪水
select e.deptno, avg(e.sal) as 'avgSal' from emp e group by e.deptno;
+--------+-------------+
| deptno | avgSal      |
+--------+-------------+
|     20 | 2175.000000 |
|     30 | 1566.666667 |
|     10 | 2916.666667 |
+--------+-------------+
3 rows in set (0.00 sec)

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

select 
	d.deptno, d.dname, t.avgSal, s.grade
from
	dept d
inner join
	(select e.deptno, avg(e.sal) as 'avgSal' from emp e group by e.deptno) as t
on
	d.deptno = t.deptno
inner join 
	salgrade s
on
	t.avgSal between s.losal and s.hisal
order by
	s.grade asc;
+--------+------------+-------------+-------+
| deptno | dname      | avgSal      | grade |
+--------+------------+-------------+-------+
|     30 | SALES      | 1566.666667 |     3 |
|     20 | RESEARCH   | 2175.000000 |     4 |
|     10 | ACCOUNTING | 2916.666667 |     4 |
+--------+------------+-------------+-------+
3 rows in set (0.00 sec)

平均薪水最低的对应的等级一定是最低的
找出最低的平均薪水值
select avg(e.sal) as 'avgSal' from emp e group by e.deptno order by avgSal asc limit 1;
+-------------+
| avgSal      |
+-------------+
| 1566.666667 |
+-------------+
1 row in set (0.00 sec)

找出最低平均薪水值对应的薪资等级
select s.grade from salgrade s where (select avg(e.sal) as 'avgSal' from emp e group by e.deptno order by avgSal asc limit 1) between s.losal and s.hisal;
+-------+
| grade |
+-------+
|     3 |
+-------+
1 row in set (0.01 sec)


在加where条件，最终为：
select 
	d.deptno, d.dname, t.avgSal, s.grade
from
	dept d
inner join
	(select e.deptno, avg(e.sal) as 'avgSal' from emp e group by e.deptno) as t
on
	d.deptno = t.deptno
inner join 
	salgrade s
on
	t.avgSal between s.losal and s.hisal
where 
    s.grade = (select s.grade from salgrade s where (select avg(e.sal) as 'avgSal' from emp e group by e.deptno order by avgSal asc limit 1) between s.losal and s.hisal)
order by
    d.deptno;
+--------+-------+-------------+-------+
| deptno | dname | avgSal      | grade |
+--------+-------+-------------+-------+
|     30 | SALES | 1566.666667 |     3 |
+--------+-------+-------------+-------+
1 row in set (0.00 sec)

七、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

比普通员工最高薪水还要高的员工一定是领导，但是领导的薪水不一定高于普通员工的最高薪水

第一步：找出领导的员工编号
select distinct e.mgr from emp e;
+------+
| mgr  |
+------+
| 7902 |
| 7698 |
| 7839 |
| 7566 |
| NULL |
| 7788 |
| 7782 |
+------+
7 rows in set (0.00 sec)

员工编号没有在以上范围内的都是普通员工

not in在使用的时候，后面小括号中记得排除NULL

select distinct e.mgr from emp e where e.mgr is not null;
+------+
| mgr  |
+------+
| 7902 |
| 7698 |
| 7839 |
| 7566 |
| 7788 |
| 7782 |
+------+
6 rows in set (0.00 sec)

第二步：找出普通员工的最高薪水
select max(e.sal) from emp e where e.empno not in (select distinct e.mgr from emp e where e.mgr is not null);
+------------+
| max(e.sal) |
+------------+
|    1600.00 |
+------------+
1 row in set (0.00 sec)

第三步：找出薪水大于1600的领导
select 
    e.empno, e.ename, e.sal
from
    emp e
where 
    e.sal > (select max(e.sal) from emp e where e.empno not in (select distinct e.mgr from emp e where e.mgr is not null));
+-------+-------+---------+
| empno | ename | sal     |
+-------+-------+---------+
|  7566 | JONES | 2975.00 |
|  7698 | BLAKE | 2850.00 |
|  7782 | CLARK | 2450.00 |
|  7788 | SCOTT | 3000.00 |
|  7839 | KING  | 5000.00 |
|  7902 | FORD  | 3000.00 |
+-------+-------+---------+
6 rows in set (0.00 sec)

select 
    e.empno, e.ename, e.sal 
from 
    emp e 
where 
    e.sal > (select max(e.sal) from emp e where e.empno not in (select distinct ifnull(e.mgr, 0) from emp e));
+-------+-------+---------+
| empno | ename | sal     |
+-------+-------+---------+
|  7566 | JONES | 2975.00 |
|  7698 | BLAKE | 2850.00 |
|  7782 | CLARK | 2450.00 |
|  7788 | SCOTT | 3000.00 |
|  7839 | KING  | 5000.00 |
|  7902 | FORD  | 3000.00 |
+-------+-------+---------+
6 rows in set (0.00 sec)

八、取得薪水最高的前五名员工

select 
    e.empno, e.ename, e.sal
from
    emp e
order by
    e.sal desc
limit
    5;
+-------+-------+---------+
| empno | ename | sal     |
+-------+-------+---------+
|  7839 | KING  | 5000.00 |
|  7788 | SCOTT | 3000.00 |
|  7902 | FORD  | 3000.00 |
|  7566 | JONES | 2975.00 |
|  7698 | BLAKE | 2850.00 |
+-------+-------+---------+
5 rows in set (0.00 sec)

九、取得薪水最高的第六到第十名员工

select 
    e.empno, e.ename, e.sal
from
    emp e
order by
    e.sal desc
limit
    5, 5;
+-------+--------+---------+
| empno | ename  | sal     |
+-------+--------+---------+
|  7782 | CLARK  | 2450.00 |
|  7499 | ALLEN  | 1600.00 |
|  7844 | TURNER | 1500.00 |
|  7934 | MILLER | 1300.00 |
|  7521 | WARD   | 1250.00 |
+-------+--------+---------+
5 rows in set (0.00 sec)

十、取得最后入职的5名员工

日期也可以降序，升序排序

select 
    e.ename, e.hiredate
from
    emp e
order by
    e.hiredate desc
limit
    0, 5;
+--------+------------+
| ename  | hiredate   |
+--------+------------+
| ADAMS  | 1987-05-23 |
| SCOTT  | 1987-04-19 |
| MILLER | 1982-01-23 |
| JAMES  | 1981-12-03 |
| FORD   | 1981-12-03 |
+--------+------------+
5 rows in set (0.00 sec)

十一、取得每个薪水等级有多少个员工

第一步：找出每个员工的薪资等级
select 
    e.ename, e.sal, s.grade
from
    emp e
inner 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 |
+--------+---------+-------+
14 rows in set (0.00 sec)

第二步：继续分组统计每个薪资等级的员工数量
select 
    s.grade, count(*)
from
    emp e
inner join
    salgrade s
on
    e.sal between s.losal and s.hisal
group by
    s.grade
order by
    s.grade asc;
+-------+----------+
| grade | count(*) |
+-------+----------+
|     1 |        3 |
|     2 |        3 |
|     3 |        2 |
|     4 |        5 |
|     5 |        1 |
+-------+----------+
5 rows in set (0.00 sec)

十二、列出所有员工及领导的名字

select 
    e.ename as '员工名', t.ename as '领导名'
from
    emp e
left outer join
    emp t
on
    e.mgr = t.empno;
+--------+--------+
| 员工名  | 领导名 |
+--------+--------+
| 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  |
+--------+--------+
14 rows in set (0.01 sec)

十三、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

emp a 员工表
emp b 领导表
连接条件：a.mgr = b.empno and a.hiredate < b.hiredate

select 
    a.empno, a.ename '员工', d.dname, a.hiredate, b.ename '领导', b.hiredate
from 
    emp a
left outer join
    emp b
on
    a.mgr = b.empno 
inner join
    dept d
on
    a.deptno = d.deptno
where
    a.hiredate < b.hiredate
order by
    a.ename asc;
+-------+-------+------------+------------+-------+------------+
| empno | 员工  | dname      | hiredate   | 领导  | hiredate   |
+-------+-------+------------+------------+-------+------------+
|  7499 | ALLEN | SALES      | 1981-02-20 | BLAKE | 1981-05-01 |
|  7698 | BLAKE | SALES      | 1981-05-01 | KING  | 1981-11-17 |
|  7782 | CLARK | ACCOUNTING | 1981-06-09 | KING  | 1981-11-17 |
|  7566 | JONES | RESEARCH   | 1981-04-02 | KING  | 1981-11-17 |
|  7369 | SMITH | RESEARCH   | 1980-12-17 | FORD  | 1981-12-03 |
|  7521 | WARD  | SALES      | 1981-02-22 | BLAKE | 1981-05-01 |
+-------+-------+------------+------------+-------+------------+
6 rows in set (0.00 sec)

select e.ename as 'staff', t.ename as 'leader' from emp e left outer join emp t on e.mgr = t.empno order by staff;

+--------+--------+
| staff  | leader |
+--------+--------+
| ADAMS  | SCOTT  |
| ALLEN  | BLAKE  |
| BLAKE  | KING   |
| CLARK  | KING   |
| FORD   | JONES  |
| JAMES  | BLAKE  |
| JONES  | KING   |
| KING   | NULL   |
| MARTIN | BLAKE  |
| MILLER | CLARK  |
| SCOTT  | JONES  |
| SMITH  | FORD   |
| TURNER | BLAKE  |
| WARD   | BLAKE  |
+--------+--------+
14 rows in set (0.00 sec)

select
    distinct e.empno, t.staff, d.dname
from
    (select e.ename as 'staff', t.ename as 'leader' from emp e left outer join emp t on e.mgr = t.empno) t
inner join
    emp e
on
    (select e.hiredate from emp e where e.ename = t.staff) < (select e.hiredate from emp e where e.ename = t.leader) and t.staff = e.ename
inner join 
    dept d
on
    e.deptno = d.deptno
order by
    t.staff asc;
+-------+-------+------------+
| empno | staff | dname      |
+-------+-------+------------+
|  7499 | ALLEN | SALES      |
|  7698 | BLAKE | SALES      |
|  7782 | CLARK | ACCOUNTING |
|  7566 | JONES | RESEARCH   |
|  7369 | SMITH | RESEARCH   |
|  7521 | WARD  | SALES      |
+-------+-------+------------+
6 rows in set (0.00 sec)

十四、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

select
    d.dname, e.ename
from
    dept d
left outer join
    emp e
on
    d.deptno = e.deptno;
+------------+--------+
| dname      | ename  |
+------------+--------+
| ACCOUNTING | MILLER |
| ACCOUNTING | KING   |
| ACCOUNTING | CLARK  |
| RESEARCH   | FORD   |
| RESEARCH   | ADAMS  |
| RESEARCH   | SCOTT  |
| RESEARCH   | JONES  |
| RESEARCH   | SMITH  |
| SALES      | JAMES  |
| SALES      | TURNER |
| SALES      | BLAKE  |
| SALES      | MARTIN |
| SALES      | WARD   |
| SALES      | ALLEN  |
| OPERATIONS | NULL   |
+------------+--------+
15 rows in set (0.00 sec)

十五、列出至少有5个员工的所有部门

select
    max(d.deptno) as '部门编号', d.dname as '部门名称', count(e.ename) as '部门人数'
from
    dept d
left outer join
    emp e
on
    d.deptno = e.deptno
group by
    d.dname
having
    count(e.ename) >= 5
order by
    部门人数 asc;
+----------+----------+----------+
| 部门编号 | 部门名称 | 部门人数 |
+----------+----------+----------+
|       20 | RESEARCH |        5 |
|       30 | SALES    |        6 |
+----------+----------+----------+
2 rows in set (0.00 sec)

十六、列出薪资比"SMITH"多的所有员工信息

select
    e.ename, e.sal 
from
    emp e
where
    e.sal > (select e.sal from emp e where e.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 |
+--------+---------+
13 rows in set (0.00 sec)

十七、列出所有"clerk"（办事员）的姓名及其部门名称，部门的人数

第一步：先求出每个部门的人数
select d.dname, count(e.ename) from dept d left outer join emp e on d.deptno = e.deptno group by d.dname;
+------------+----------------+
| dname      | count(e.ename) |
+------------+----------------+
| ACCOUNTING |              3 |
| RESEARCH   |              5 |
| SALES      |              6 |
| OPERATIONS |              0 |
+------------+----------------+
4 rows in set (0.00 sec)

第二步：进行内连接
select
    e.ename, e.job, d.dname, t.num
from
    emp e
inner join
    dept d
on
    e.deptno = d.deptno
inner join
    (select d.dname, count(e.ename) as 'num' from dept d left outer join emp e on d.deptno = e.deptno group by d.dname) as t
on
    d.dname = t.dname
where
    e.job = 'CLERK';
+--------+-------+------------+-----+
| ename  | job   | dname      | num |
+--------+-------+------------+-----+
| SMITH  | CLERK | RESEARCH   |   5 |
| ADAMS  | CLERK | RESEARCH   |   5 |
| JAMES  | CLERK | SALES      |   6 |
| MILLER | CLERK | ACCOUNTING |   3 |
+--------+-------+------------+-----+
4 rows in set (0.01 sec)

十八、列出最低薪资大于1500的各种工作及从事此工作的全部员工人数

第一种方法：

select
    e.job, count(e.ename)
from
    emp e
group by
    e.job
having
    min(e.sal) > 1500;
+-----------+----------------+
| job       | count(e.ename) |
+-----------+----------------+
| MANAGER   |              3 |
| ANALYST   |              2 |
| PRESIDENT |              1 |
+-----------+----------------+
3 rows in set (0.00 sec)

第二种方法：

第一步：找出最低薪资大于1500的岗位
select 
    e.job, min(e.sal) as 'minSal'
from
    emp e
group by
    e.job
having
    min(e.sal) > 1500;
+-----------+---------+
| job       | minSal  |
+-----------+---------+
| MANAGER   | 2450.00 |
| ANALYST   | 3000.00 |
| PRESIDENT | 5000.00 |
+-----------+---------+
3 rows in set (0.00 sec)

第二步：进行子查询
select
    e.job, count(*)
from
    emp e
where
    e.job in 
    (select 
        e.job
    from
        emp e
    group by
        e.job
    having
        min(e.sal) > 1500)
group by
    e.job;
+-----------+----------+
| job       | count(*) |
+-----------+----------+
| MANAGER   |        3 |
| ANALYST   |        2 |
| PRESIDENT |        1 |
+-----------+----------+
3 rows in set (0.00 sec)

十九、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

第一种方法：

select
    e.ename, d.dname
from
    emp e
inner join
    dept d
on
    e.deptno = d.deptno
where
    d.dname = 'SALES';
+--------+-------+
| ename  | dname |
+--------+-------+
| ALLEN  | SALES |
| WARD   | SALES |
| MARTIN | SALES |
| BLAKE  | SALES |
| TURNER | SALES |
| JAMES  | SALES |
+--------+-------+
6 rows in set (0.00 sec)

第二种方法：

select
    e.ename
from
    emp e
where
    e.deptno = (select d.deptno from dept d where d.dname = 'SALES');
+--------+
| ename  |
+--------+
| ALLEN  |
| WARD   |
| MARTIN |
| BLAKE  |
| TURNER |
| JAMES  |
+--------+
6 rows in set (0.01 sec)

二十、列出薪资高于公司平均薪水的所有员工，所在部门，上级领导，雇员的工资等级

第一步：求公司平均薪资
select
    avg(e.sal)
from
    emp e;
+-------------+
| avg(e.sal)  |
+-------------+
| 2073.214286 |
+-------------+
1 row in set (0.01 sec)

select
    e.ename as '员工名', d.dname as '部门名称', t.ename as '领导名', e.sal as '薪资', s.grade as '薪资等级'
from
    emp e
inner join
    dept d
on
    e.deptno = d.deptno
left outer join
    emp t
on
    e.mgr = t.empno
inner join
    salgrade s
on
    e.sal between s.losal and s.hisal
where
    e.sal > 
    (select
        avg(e.sal)
    from
        emp e);
+--------+------------+--------+---------+----------+
| 员工名 | 部门名称   | 领导名 | 薪资    | 薪资等级 |
+--------+------------+--------+---------+----------+
| FORD   | RESEARCH   | JONES  | 3000.00 |        4 |
| SCOTT  | RESEARCH   | JONES  | 3000.00 |        4 |
| CLARK  | ACCOUNTING | KING   | 2450.00 |        4 |
| BLAKE  | SALES      | KING   | 2850.00 |        4 |
| JONES  | RESEARCH   | KING   | 2975.00 |        4 |
| KING   | ACCOUNTING | NULL   | 5000.00 |        5 |
+--------+------------+--------+---------+----------+
6 rows in set (0.00 sec)

二十一、列出与"SCOTT"从事相同工作的所有员工及部门名称

select 
    e.job
from
    emp e
where
    e.ename = 'SCOTT';
+---------+
| job     |
+---------+
| ANALYST |
+---------+
1 row in set (0.00 sec)

select    
    e.ename, e.job, d.dname
from
    emp e
inner join
    dept d
on
    e.deptno = d.deptno
where
    e.job = (
        select 
            e.job
        from
            emp e
        where
            e.ename = 'SCOTT')
and
    e.ename != 'SCOTT';
+-------+---------+----------+
| ename | job     | dname    |
+-------+---------+----------+
| FORD  | ANALYST | RESEARCH |
+-------+---------+----------+
1 row in set (0.00 sec)

二十二、列出薪资等于部门30中员工的薪资的其他员工的姓名和薪资

第一种写法：

select
    *
from
    emp e
where
    e.deptno = 30;
+-------+--------+----------+------+------------+---------+---------+--------+
| EMPNO | ENAME  | JOB      | MGR  | HIREDATE   | SAL     | COMM    | DEPTNO |
+-------+--------+----------+------+------------+---------+---------+--------+
|  7499 | ALLEN  | SALESMAN | 7698 | 1981-02-20 | 1600.00 |  300.00 |     30 |
|  7521 | WARD   | SALESMAN | 7698 | 1981-02-22 | 1250.00 |  500.00 |     30 |
|  7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 |     30 |
|  7698 | BLAKE  | MANAGER  | 7839 | 1981-05-01 | 2850.00 |    NULL |     30 |
|  7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 |    0.00 |     30 |
|  7900 | JAMES  | CLERK    | 7698 | 1981-12-03 |  950.00 |    NULL |     30 |
+-------+--------+----------+------+------------+---------+---------+--------+
6 rows in set (0.00 sec)

select
    *
from
    emp e
where 
    e.sal in (select e.sal from emp e where e.deptno = 30)
and
    e.ename not in (select e.ename from emp e where e.deptno = 30);

Empty set (0.02 sec)

第二种写法：

select
    e.ename, e.sal
from
    emp e
where
    e.sal in (select distinct e.sal from emp e where e.deptno = 30)
and
    e.deptno != 30;

Empty set (0.00 sec)

二十三、列出薪资高于在部门30工作的所有员工的薪资的员工姓名和薪资，部门名称

第一步：找出在30部门工作的所有员工的最高薪资
select 
    max(e.sal)
from
    emp e
where
    e.deptno = 30;
+------------+
| max(e.sal) |
+------------+
|    2850.00 |
+------------+
1 row in set (0.00 sec)

第二步：找出高于该薪资的员工和部门名称
select 
    e.ename as '姓名', d.dname as '部门名称'
from
    emp e
inner join
    dept d
on
    e.deptno = d.deptno
where
    e.sal > (
        select 
            max(e.sal)
        from
            emp e
        where
            e.deptno = 30
    );
+-------+------------+
| 姓名  | 部门名称   |
+-------+------------+
| JONES | RESEARCH   |
| SCOTT | RESEARCH   |
| FORD  | RESEARCH   |
| KING  | ACCOUNTING |
+-------+------------+
4 rows in set (0.00 sec)

二十四、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

select
    d.deptno, max(d.dname), count(e.ename), avg(e.sal)
from
    dept d
left outer join
    emp e
on
    d.deptno = e.deptno
group by
    d.deptno;
+--------+--------------+----------------+-------------+
| deptno | max(d.dname) | count(e.ename) | avg(e.sal)  |
+--------+--------------+----------------+-------------+
|     10 | ACCOUNTING   |              3 | 2916.666667 |
|     20 | RESEARCH     |              5 | 2175.000000 |
|     30 | SALES        |              6 | 1566.666667 |
|     40 | OPERATIONS   |              0 |        NULL |
+--------+--------------+----------------+-------------+
4 rows in set (0.00 sec)

select
    d.deptno as '部门编号', d.dname as '部门名称', d.loc as '部门地址', count(e.ename) as '部门人数', ifnull(avg(e.sal), 0) as '平均薪资'
from
    dept d
left outer join
    emp e
on
    d.deptno = e.deptno
group by
    d.deptno, d.dname, d.loc;
+----------+------------+----------+----------+-------------+
| 部门编号 | 部门名称   | 部门地址 | 部门人数 | 平均薪资    |
+----------+------------+----------+----------+-------------+
|       10 | ACCOUNTING | NEW YORK |        3 | 2916.666667 |
|       20 | RESEARCH   | DALLAS   |        5 | 2175.000000 |
|       30 | SALES      | CHICAGO  |        6 | 1566.666667 |
|       40 | OPERATIONS | BOSTON   |        0 |    0.000000 |
+----------+------------+----------+----------+-------------+
4 rows in set (0.00 sec)

select 
	d.deptno as '部门编号', d.dname as '部门名称', count(e.ename) as '部门员工数', ifnull(avg(e.sal), 0) as '平均薪资', ifnull(avg(timestampdiff(year, e.hiredate, now())), 0) as '平均服务期限'
from
	dept d
left outer join
	emp e
on
	d.deptno = e.deptno
group by
	d.deptno, d.dname;
+----------+------------+------------+-------------+--------------+
| 部门编号 | 部门名称   | 部门员工数 | 平均薪资    | 平均服务期限 |
+----------+------------+------------+-------------+--------------+
|       10 | ACCOUNTING |          3 | 2916.666667 |      41.3333 |
|       20 | RESEARCH   |          5 | 2175.000000 |      39.4000 |
|       30 | SALES      |          6 | 1566.666667 |      41.8333 |
|       40 | OPERATIONS |          0 |    0.000000 |       0.0000 |
+----------+------------+------------+-------------+--------------+
4 rows in set (0.00 sec)

二十五、列出所有员工的姓名，部门名称和工资

select
    e.ename, d.dname, e.sal
from
    emp e
inner join
    dept d
on
    e.deptno = d.deptno;
+--------+------------+---------+
| ename  | dname      | sal     |
+--------+------------+---------+
| SMITH  | RESEARCH   |  800.00 |
| ALLEN  | SALES      | 1600.00 |
| WARD   | SALES      | 1250.00 |
| JONES  | RESEARCH   | 2975.00 |
| MARTIN | SALES      | 1250.00 |
| BLAKE  | SALES      | 2850.00 |
| CLARK  | ACCOUNTING | 2450.00 |
| SCOTT  | RESEARCH   | 3000.00 |
| KING   | ACCOUNTING | 5000.00 |
| TURNER | SALES      | 1500.00 |
| ADAMS  | RESEARCH   | 1100.00 |
| JAMES  | SALES      |  950.00 |
| FORD   | RESEARCH   | 3000.00 |
| MILLER | ACCOUNTING | 1300.00 |
+--------+------------+---------+
14 rows in set (0.00 sec)

二十六、列出所有部门的详细信息和人数

select
    d.deptno '部门编号', d.dname '部门名称', d.loc '部门地址', count(e.ename) '部门人数'
from
    dept d
left outer join
    emp e
on
    d.deptno = e.deptno
group by
    d.deptno, d.dname, d.loc;

+----------+------------+----------+----------+
| 部门编号 | 部门名称   | 部门地址 | 部门人数 |
+----------+------------+----------+----------+
|       10 | ACCOUNTING | NEW YORK |        3 |
|       20 | RESEARCH   | DALLAS   |        5 |
|       30 | SALES      | CHICAGO  |        6 |
|       40 | OPERATIONS | BOSTON   |        0 |
+----------+------------+----------+----------+
4 rows in set (0.00 sec)

二十七、列出各种工作的最低工资及从事此工作的员工姓名

select
    e.job, min(e.sal)
from
    emp e
group by
    e.job;
+-----------+------------+
| job       | min(e.sal) |
+-----------+------------+
| CLERK     |     800.00 |
| SALESMAN  |    1250.00 |
| MANAGER   |    2450.00 |
| ANALYST   |    3000.00 |
| PRESIDENT |    5000.00 |
+-----------+------------+
5 rows in set (0.01 sec)

select
    e.ename, t.*
from
    emp e
inner join
    (select
        e.job, min(e.sal) as 'minSal'
    from
        emp e
    group by
        e.job) as 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 |
+--------+-----------+---------+
7 rows in set (0.01 sec)

二十八、列出各个部门的"MANAGER"（领导）的最低薪资

select
    e.deptno, e.ename, e.job, min(e.sal)
from
    emp e
where
    e.job = 'MANAGER'
group by
    e.deptno, e.ename, e.job;
+--------+-------+---------+------------+
| deptno | ename | job     | min(e.sal) |
+--------+-------+---------+------------+
|     20 | JONES | MANAGER |    2975.00 |
|     30 | BLAKE | MANAGER |    2850.00 |
|     10 | CLARK | MANAGER |    2450.00 |
+--------+-------+---------+------------+
3 rows in set (0.00 sec)

二十九、列出所有员工的年工资，按年薪从低到高排序

select
    e.ename, (e.sal + ifnull(e.comm, 0)) * 12 as 'yearsal'
from
    emp e
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 |
| SCOTT  | 36000.00 |
| FORD   | 36000.00 |
| KING   | 60000.00 |
+--------+----------+
14 rows in set (0.00 sec)

三十、求出员工领导的薪水超过3000的员工名称及领导名称

select
    a.ename '员工名', a.sal '员工薪资', b.ename '领导名', b.sal '领导薪资'
from
    emp a
left outer join
    emp b
on
    a.mgr = b.empno
where
    b.sal > 3000;
+--------+----------+--------+----------+
| 员工名 | 员工薪资 | 领导名 | 领导薪资 |
+--------+----------+--------+----------+
| JONES  |  2975.00 | KING   |  5000.00 |
| BLAKE  |  2850.00 | KING   |  5000.00 |
| CLARK  |  2450.00 | KING   |  5000.00 |
+--------+----------+--------+----------+
3 rows in set (0.03 sec)

三十一、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

select
    d.deptno '部门编号', d.dname '部门名称', ifnull(sum(e.sal), 0) '工资合计', count(e.ename) '部门人数'
from
    dept d
left outer join
    emp e
on
    d.deptno = e.deptno
where
    d.dname like '%S%'
group by
    d.deptno, d.dname;

+----------+------------+----------+----------+
| 部门编号 | 部门名称   | 工资合计 | 部门人数 |
+----------+------------+----------+----------+
|       20 | RESEARCH   | 10875.00 |        5 |
|       30 | SALES      |  9400.00 |        6 |
|       40 | OPERATIONS |     0.00 |        0 |
+----------+------------+----------+----------+
3 rows in set (0.00 sec)

三十二、给任职日期超过30年的员工加薪10%

select
    e.ename '姓名', e.sal '当前薪资', timestampdiff(year, e.hiredate, now()) '任职年限', e.sal * 1.1 '调整后薪资'
from
    emp e
where
    timestampdiff(year, e.hiredate, now()) > 30;
+--------+----------+----------+------------+
| 姓名   | 当前薪资 | 任职年限 | 调整后薪资 |
+--------+----------+----------+------------+
| SMITH  |   800.00 |       42 |     880.00 |
| ALLEN  |  1600.00 |       42 |    1760.00 |
| WARD   |  1250.00 |       42 |    1375.00 |
| JONES  |  2975.00 |       42 |    3272.50 |
| MARTIN |  1250.00 |       42 |    1375.00 |
| BLAKE  |  2850.00 |       42 |    3135.00 |
| CLARK  |  2450.00 |       42 |    2695.00 |
| SCOTT  |  3000.00 |       36 |    3300.00 |
| KING   |  5000.00 |       41 |    5500.00 |
| TURNER |  1500.00 |       42 |    1650.00 |
| ADAMS  |  1100.00 |       36 |    1210.00 |
| JAMES  |   950.00 |       41 |    1045.00 |
| FORD   |  3000.00 |       41 |    3300.00 |
| MILLER |  1300.00 |       41 |    1430.00 |
+--------+----------+----------+------------+
14 rows in set (0.00 sec)