MySQL数据库练习【三】

一、建库建表-数据准备

create database company;

use company;

-- 创建部门表
DROP TABLE IF EXISTS dept; 
CREATE TABLE `dept` (
  `deptno` int(11) PRIMARY KEY NOT NULL COMMENT '部门编号',
  `dname` varchar(14) NOT NULL COMMENT '部门名称',
  `loc` varchar(13) NOT NULL COMMENT '部门所在地'
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='部门表';
 
-- 向部门表插入数据
INSERT INTO dept VALUES (10,'ACCOUNTING','NEW YORK'),
(20,'RESEARCH','DALLAS'),
(30,'SALES','CHICAGO'),
(40,'OPERATIONS','BOSTON');
 
-- 创建员工表
DROP TABLE IF EXISTS emp;
CREATE TABLE `emp` (
  `empno` int(11) PRIMARY KEY NOT NULL COMMENT '员工编号',
  `ename` varchar(10) DEFAULT NULL COMMENT '员工姓名',
  `job` varchar(9) DEFAULT NULL COMMENT '工作岗位',
  `mgr` int(11) DEFAULT NULL COMMENT '直属领导',
  `hiredate` date DEFAULT NULL COMMENT '入职时间',
  `sal` double DEFAULT NULL COMMENT '工资',
  `comm` double DEFAULT NULL COMMENT '奖金',
  `deptno` int(11) DEFAULT NULL COMMENT '所属部门'
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='员工表';

-- 向员工表插入数据
INSERT INTO emp VALUES(7369,'SMITH','CLERK',7902,"1980-12-17",800,NULL,20),
(7499,'ALLEN','SALESMAN',7698,'1981-02-20',1600,300,30),
(7521,'WARD','SALESMAN',7698,'1981-02-22',1250,500,30),
(7566,'JONES','MANAGER',7839,'1981-04-02',2975,NULL,20),
(7654,'MARTIN','SALESMAN',7698,'1981-09-28',1250,1400,30),
(7698,'BLAKE','MANAGER',7839,'1981-05-01',2850,NULL,30),
(7782,'CLARK','MANAGER',7839,'1981-06-09',2450,NULL,10),
(7788,'SCOTT','ANALYST',7566,'1987-07-03',3000,NULL,20),
(7839,'KING','PRESIDENT',NULL,'1981-11-17',5000,NULL,10),
(7844,'TURNER','SALESMAN',7698,'1981-09-08',1500,0,30),
(7876,'ADAMS','CLERK',7788,'1987-07-13',1100,NULL,20),
(7900,'JAMES','CLERK',7698,'1981-12-03',950,NULL,30),
(7902,'FORD','ANALYST',7566,'1981-12-03',3000,NULL,20),
(7934,'MILLER','CLERK',7782,'1981-01-23',1300,NULL,10);
 
 
-- 创建工资等级表
DROP TABLE IF EXISTS salgrade;
CREATE TABLE `salgrade` (
  `grade` int(11) DEFAULT NULL COMMENT '等级',
  `losal` double DEFAULT NULL COMMENT '最低工资',
  `hisal` double DEFAULT NULL COMMENT '最高工资'
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='工资等级表';
 
-- 向工资等级表插入数据
INSERT INTO salgrade VALUES (1,700,1200),(2,1201,1400),(3,1401,2000),(4,2001,3000),(5,3001,9999);

员工表emp	部门表dept	工资等级表salgrade
empno：员工编号	deptno：部门编号	grade：等级
ename：员工姓名	dname：部门名称	losal：最低工资
job：工作岗位	loc：部门所在地	hisal：最高工资
mgr：直属领导
hiredate：入职时间
sal：工资
comm：奖金
deptno：所属部门

empno	ename	job	mgr	hiredate	sal	comm	deptno
7369	SMITH	CLERK	7902	1980-12-17	800	NULL	20
7499	ALLEN	SALESMAN	7698	1981-02-20	1600	300	30
7521	WARD	SALESMAN	7698	1981-02-22	1250	500	30
7566	JONES	MANAGER	7839	1981-04-02	2975	NULL	20
7654	MARTIN	SALESMAN	7698	1981-09-28	1250	1400	30
7698	BLAKE	MANAGER	7839	1981-05-01	2850	NULL	30
7782	CLARK	MANAGER	7839	1981-06-09	2450	NULL	10
7788	SCOTT	ANALYST	7566	1987-07-03	3000	NULL	20
7839	KING	PRESIDENT	NULL	1981-11-17	5000	NULL	10
7844	TURNER	SALESMAN	7698	1981-09-08	1500	0	30
7876	ADAMS	CLERK	7788	1987-07-13	1100	NULL	20
7900	JAMES	CLERK	7698	1981-12-03	950	NULL	30
7902	FORD	ANALYST	7566	1981-12-03	3000	NULL	20
7934	MILLER	CLERK	7782	1981-01-23	1300	NULL	10

deptno	dname	loc
10	ACCOUNTING	NEW YORK
20	RESEARCH	DALLAS
30	SALES	CHICAGO
40	OPERATIONS	BOSTON

grade	losal	hisal
1	700	1200
2	1201	1400
3	1401	2000
4	2001	3000
5	3001	9999

二、动力节点—Mysql—经典34道习题

1、查询每个部门最高薪水的人员名称
2、哪些人的薪水在部门的平均薪水之上
3、取得部门中（所有人的）平均的薪水等级
4、不准用组函数（Max），查询最高薪水
5、查询平均薪水最高的部门的部门编号
6、查询平均薪水最高的部门的部门名称
7、求平均薪水的等级最低的部门的部门名称
8、查询比普通员工(员工代表没有在 mgr 字段上出现的) 的最高薪水还要高的领导人姓名
9、查询薪水最高的前五名员工
10、查询薪水最高的第六到第十名员工
11、查询查询最后入职的 5 名员工
12、查询每个薪水等级有多少员工
13、面试题：
14、列出所有员工及领导的姓名
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
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
17、列出至少有 5 个员工的所有部门
18、列出薪金比"SMITH" 多的所有员工信息
19、列出所有"CLERK"( 办事员) 的姓名及其部门名称, 部门的人数
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
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
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
23、列出与"SCOTT" 从事相同工作的所有员工及部门名称
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
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
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
26、在mysql当中怎么计算两个日期的“年差”，差了多少年【知识点】
27、列出所有员工的姓名、部门名称和工资
28、列出所有部门的详细信息和人数
29、列出各种工作的最低工资及从事此工作的雇员姓名
30、列出各个部门的 MANAGER( 领导) 的最低薪金
31、列出所有员工的 年工资, 按 年薪从低到高排序
32、求出员工领导的薪水超过3000的员工名称与领导
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
34、给任职日期超过 30 年的员工加薪 10%

三、动力节点—Mysql—经典34道答案

3.1、查询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)
select
	deptno,
	max(sal)
from emp
group by deptno;

mysql> select
    -> deptno,
    -> max(sal)
    -> from emp
    -> group by deptno;
+--------+----------+
| deptno | max(sal) |
+--------+----------+
|     10 |     5000 |
|     20 |     3000 |
|     30 |     2850 |
+--------+----------+
3 rows in set (0.00 sec)

-- 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
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;

mysql> 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 |
| SCOTT |     20 |   3000 |
| KING  |     10 |   5000 |
| FORD  |     20 |   3000 |
+-------+--------+--------+
4 rows in set (0.00 sec)

select
	e1.ename,
	e1.sal,
	count(distinct e2.sal) rank
from emp e1
join emp e2 on e1.deptno = e2.deptno and e1.sal <= e2.sal
group by e1.empno
order by rank;

mysql> select
    -> e1.ename,
    -> e1.sal,
    -> count(distinct e2.sal) rank
    -> from emp e1
    -> join emp e2 on e1.deptno = e2.deptno and e1.sal <= e2.sal
    -> group by e1.empno
    -> order by rank;
+--------+------+------+
| ename  | sal  | rank |
+--------+------+------+
| SCOTT  | 3000 |    1 |
| FORD   | 3000 |    1 |
| KING   | 5000 |    1 |
| BLAKE  | 2850 |    1 |
| JONES  | 2975 |    2 |
| ALLEN  | 1600 |    2 |
| CLARK  | 2450 |    2 |
| MILLER | 1300 |    3 |
| TURNER | 1500 |    3 |
| ADAMS  | 1100 |    3 |
| WARD   | 1250 |    4 |
| MARTIN | 1250 |    4 |
| SMITH  |  800 |    4 |
| JAMES  |  950 |    5 |
+--------+------+------+
14 rows in set (0.00 sec)

select
	e1.ename,
	e1.sal,
	count(distinct e2.sal) rank
from emp e1
join emp e2 on e1.deptno = e2.deptno and e1.sal <= e2.sal
group by e1.empno
having rank = 1
order by rank;

mysql> select
    -> e1.ename,
    -> e1.sal,
    -> count(distinct e2.sal) rank
    -> from emp e1
    -> join emp e2 on e1.deptno = e2.deptno and e1.sal <= e2.sal
    -> group by e1.empno
    -> having rank = 1
    -> order by rank;
+-------+------+------+
| ename | sal  | rank |
+-------+------+------+
| SCOTT | 3000 |    1 |
| FORD  | 3000 |    1 |
| KING  | 5000 |    1 |
| BLAKE | 2850 |    1 |
+-------+------+------+
4 rows in set (0.01 sec)

3.2、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
select
	e.deptno,
	avg(e.sal)
from emp e
group by e.deptno;

mysql> select
    -> e.deptno,
    -> avg(e.sal)
    -> from emp e
    -> group by e.deptno;
+--------+--------------------+
| deptno | avg(e.sal)         |
+--------+--------------------+
|     10 | 2916.6666666666665 |
|     20 |               2175 |
|     30 | 1566.6666666666667 |
+--------+--------------------+
3 rows in set (0.00 sec)

-- 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
select
	e.ename,
	e.sal,
	t.deptno,
	round(t.avgsal,2) '平均薪资'
from emp e
join (select deptno,avg(sal) avgsal from emp group by deptno) t
on e.deptno = t.deptno and e.sal > t.avgsal
order by e.deptno;

mysql> select
    -> e.ename,
    -> e.sal,
    -> t.deptno,
    -> round(t.avgsal,2) '平均薪资'
    -> from emp e
    -> join (select deptno,avg(sal) avgsal from emp group by deptno) t
    -> on e.deptno = t.deptno and e.sal > t.avgsal
    -> order by e.deptno;
+-------+------+--------+--------------+
| ename | sal  | deptno | 平均薪资     |
+-------+------+--------+--------------+
| KING  | 5000 |     10 |      2916.67 |
| JONES | 2975 |     20 |      2175.00 |
| SCOTT | 3000 |     20 |      2175.00 |
| FORD  | 3000 |     20 |      2175.00 |
| ALLEN | 1600 |     30 |      1566.67 |
| BLAKE | 2850 |     30 |      1566.67 |
+-------+------+--------+--------------+
6 rows in set (0.00 sec)

3.3、查询部门中（所有人的）平均的薪水等级

3.3.1.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。

-- 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
select
	e.ename,
	e.sal,
	e.deptno,
	s.grade
from emp e
join salgrade s on e.sal between s.losal and s.hisal;

mysql> 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 |
+--------+------+--------+-------+
| SMITH  |  800 |     20 |     1 |
| ALLEN  | 1600 |     30 |     3 |
| WARD   | 1250 |     30 |     2 |
| JONES  | 2975 |     20 |     4 |
| MARTIN | 1250 |     30 |     2 |
| BLAKE  | 2850 |     30 |     4 |
| CLARK  | 2450 |     10 |     4 |
| SCOTT  | 3000 |     20 |     4 |
| KING   | 5000 |     10 |     5 |
| TURNER | 1500 |     30 |     3 |
| ADAMS  | 1100 |     20 |     1 |
| JAMES  |  950 |     30 |     1 |
| FORD   | 3000 |     20 |     4 |
| MILLER | 1300 |     10 |     2 |
+--------+------+--------+-------+
14 rows in set (0.00 sec)

-- 第二步：基于以上的结果继续按照deptno分组，求grade的平均值
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;

mysql> 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 |
+--------+--------------+
3 rows in set (0.00 sec)

3.3.2.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

select
	e.deptno,
	avg(e.sal)
from emp e
group by e.deptno;

mysql> select
    -> e.deptno,
    -> avg(e.sal)
    -> from emp e
    -> group by e.deptno;
+--------+--------------------+
| deptno | avg(e.sal)         |
+--------+--------------------+
|     10 | 2916.6666666666665 |
|     20 |               2175 |
|     30 | 1566.6666666666667 |
+--------+--------------------+
3 rows in set (0.00 sec)

select
	t.deptno,
	round(t.avgsal,2),
	s.grade
from (select deptno,avg(sal) avgsal from emp group by deptno) t
join salgrade s on t.avgsal between s.losal and s.hisal;

mysql> select
    -> t.deptno,
    -> round(t.avgsal,2),
    -> s.grade
    -> from (select deptno,avg(sal) avgsal from emp group by deptno) t
    -> join salgrade s on t.avgsal between s.losal and s.hisal;
+--------+-------------------+-------+
| deptno | round(t.avgsal,2) | grade |
+--------+-------------------+-------+
|     10 |           2916.67 |     4 |
|     20 |           2175.00 |     4 |
|     30 |           1566.67 |     3 |
+--------+-------------------+-------+
3 rows in set (0.00 sec)

3.4、不准用组函数（Max），查询最高薪水

select ename,sal from emp order by sal desc limit 1;

mysql> select ename,sal from emp order by sal desc limit 1;
+-------+------+
| ename | sal  |
+-------+------+
| KING  | 5000 |
+-------+------+
1 row in set (0.00 sec)

select max(sal) from emp;

mysql> select max(sal) from emp;
+----------+
| max(sal) |
+----------+
|     5000 |
+----------+
1 row in set (0.01 sec)

select
	ename,
	sal
from emp
where sal not in (select distinct a.sal from emp a join emp b on a.sal < b.sal);

mysql> select
    -> ename,
    -> sal
    -> from emp
    -> where sal not in (select distinct a.sal from emp a join emp b on a.sal < b.sal);
+-------+------+
| ename | sal  |
+-------+------+
| KING  | 5000 |
+-------+------+
1 row in set (0.00 sec)

3.5、查询平均薪水最高的部门的部门编号

-- 第一步：找出每个部门的平均薪水
select deptno,round(avg(sal),2) avgsal from emp group by deptno;

mysql> select deptno,round(avg(sal),2) avgsal from emp group by deptno;
+--------+---------+
| deptno | avgsal  |
+--------+---------+
|     10 | 2916.67 |
|     20 | 2175.00 |
|     30 | 1566.67 |
+--------+---------+
3 rows in set (0.01 sec)

-- 第二步：降序选第一个
select deptno,round(avg(sal),2) avgsal from emp group by deptno order by avgsal desc limit 1;

mysql> select deptno,round(avg(sal),2) avgsal from emp group by deptno order by avgsal desc limit 1;
+--------+---------+
| deptno | avgsal  |
+--------+---------+
|     10 | 2916.67 |
+--------+---------+
1 row in set (0.00 sec)

select
	deptno,
	avg(sal) avgsal
from emp
group by deptno
having avgsal = (select max(t.avgsal) from (select avg(sal) avgsal from emp group by deptno) t); -- 使用having语句过滤

mysql> select
    -> deptno,
    -> avg(sal) avgsal
    -> from emp
    -> group by deptno
    -> having avgsal = (select max(t.avgsal) from (select avg(sal) avgsal from emp group by deptno) t);
+--------+--------------------+
| deptno | avgsal             |
+--------+--------------------+
|     10 | 2916.6666666666665 |
+--------+--------------------+
1 row in set (0.00 sec)

3.6、查询平均薪水最高的部门的部门名称

select
	e1.deptno,
	d.dname,
	e1.avgsal
from (select deptno,avg(sal) avgsal from emp group by deptno) e1
join dept d on e1.deptno = d.deptno
having e1.avgsal = (select max(e.avgsal)from (select deptno,avg(sal) avgsal from emp group by deptno) e);

mysql> select
    -> e1.deptno,
    -> d.dname,
    -> e1.avgsal
    -> from (select deptno,avg(sal) avgsal from emp group by deptno) e1
    -> join dept d on e1.deptno = d.deptno
    -> having e1.avgsal = (select max(e.avgsal)from (select deptno,avg(sal) avgsal from emp group by deptno) e);
+--------+------------+--------------------+
| deptno | dname      | avgsal             |
+--------+------------+--------------------+
|     10 | ACCOUNTING | 2916.6666666666665 |
+--------+------------+--------------------+
1 row in set (0.00 sec)

select
	d.dname,
	avg(e.sal) avgsal
from emp e
join dept d on e.deptno = d.deptno
group by e.deptno
order by avgsal desc
limit 1;

mysql> select
    -> d.dname,
    -> avg(e.sal) avgsal
    -> from emp e
    -> join dept d on e.deptno = d.deptno
    -> group by e.deptno
    -> order by avgsal desc
    -> limit 1;
+------------+--------------------+
| dname      | avgsal             |
+------------+--------------------+
| ACCOUNTING | 2916.6666666666665 |
+------------+--------------------+
1 row in set (0.00 sec)

3.7、求平均薪水的等级最低的部门的部门名称

select
	e.avgsal,
	s.grade
from (select deptno,avg(sal) avgsal from emp group by deptno) e
join salgrade s on e.avgsal between s.losal and s.hisal
group by deptno;

mysql> select
    -> e.avgsal,
    -> s.grade
    -> from (select deptno,avg(sal) avgsal from emp group by deptno) e
    -> join salgrade s on e.avgsal between s.losal and s.hisal
    -> group by deptno;
+--------------------+-------+
| avgsal             | grade |
+--------------------+-------+
| 2916.6666666666665 |     4 |
|               2175 |     4 |
| 1566.6666666666667 |     3 |
+--------------------+-------+
3 rows in set (0.00 sec)

select
	e.avgsal,
	s.grade,
	d.deptno,
	d.dname
from (select deptno,avg(sal) avgsal from emp group by deptno) e
join dept d on e.deptno = d.deptno
join salgrade s on e.avgsal between s.losal and s.hisal
group by deptno
order by s.grade asc limit 1;

mysql> select
    -> e.avgsal,
    -> s.grade,
    -> d.deptno,
    -> d.dname
    -> from (select deptno,avg(sal) avgsal from emp group by deptno) e
    -> join dept d on e.deptno = d.deptno
    -> join salgrade s on e.avgsal between s.losal and s.hisal
    -> group by deptno
    -> order by s.grade asc limit 1;
+--------------------+-------+--------+-------+
| avgsal             | grade | deptno | dname |
+--------------------+-------+--------+-------+
| 1566.6666666666667 |     3 |     30 | SALES |
+--------------------+-------+--------+-------+
1 row in set (0.00 sec)

3.8、查询比普通员工(员工代表没有在 mgr 字段上出现的) 的最高薪水还要高的领导人姓名

-- 普通员工没有出现在mgr上，查找mgr
select distinct mgr from emp where mgr is not null;

mysql> select distinct mgr from emp where mgr is not null;
+------+
| mgr  |
+------+
| 7902 |
| 7698 |
| 7839 |
| 7566 |
| 7788 |
| 7782 |
+------+
6 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

-- 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
select max(sal)
from emp
where empno not in (select distinct mgr from emp where mgr is not null);

mysql> select max(sal)
    -> from emp
    -> where empno not in (select distinct mgr from emp where mgr is not null);
+----------+
| max(sal) |
+----------+
|     1600 |
+----------+
1 row in set (0.00 sec)

-- 第二步：找出高于1600的,比普通员工最高薪水的经理人名字
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));

mysql> 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 |
| BLAKE | 2850 |
| CLARK | 2450 |
| SCOTT | 3000 |
| KING  | 5000 |
| FORD  | 3000 |
+-------+------+
6 rows in set (0.00 sec)

3.9、查询薪水最高的前五名员工

select 
	ename,
	sal 
from emp 
order by sal desc 
limit 5;

mysql> select 
    -> ename,
    -> sal 
    -> from emp 
    -> order by sal desc 
    -> limit 5;
+-------+------+
| ename | sal  |
+-------+------+
| KING  | 5000 |
| FORD  | 3000 |
| SCOTT | 3000 |
| JONES | 2975 |
| BLAKE | 2850 |
+-------+------+
5 rows in set (0.00 sec)

mysql> select 
    -> ename,
    -> sal 
    -> from emp 
    -> order by sal desc 
    -> limit 0,5;
+-------+------+
| ename | sal  |
+-------+------+
| KING  | 5000 |
| FORD  | 3000 |
| SCOTT | 3000 |
| JONES | 2975 |
| BLAKE | 2850 |
+-------+------+
5 rows in set (0.00 sec)

3.10、查询薪水最高的第六到第十名员工

select 
	ename,
	sal 
from emp 
order by sal desc 
limit 5,5;

mysql> select 
    -> ename,
    -> sal 
    -> from emp 
    -> order by sal desc 
    -> limit 5,5;
+--------+------+
| ename  | sal  |
+--------+------+
| CLARK  | 2450 |
| ALLEN  | 1600 |
| TURNER | 1500 |
| MILLER | 1300 |
| WARD   | 1250 |
+--------+------+
5 rows in set (0.00 sec)

3.11、查询最后入职的 5 名员工

select
	ename,
	hiredate
from emp
order by hiredate desc limit 0,5;

mysql> select
    -> ename,
    -> hiredate
    -> from emp
    -> order by hiredate desc limit 0,5;
+-------+------------+
| ename | hiredate   |
+-------+------------+
| ADAMS | 1987-07-13 |
| SCOTT | 1987-07-03 |
| JAMES | 1981-12-03 |
| FORD  | 1981-12-03 |
| KING  | 1981-11-17 |
+-------+------------+
5 rows in set (0.00 sec)

3.12、查询每个薪水等级有多少员工

-- 第一步：找出每个员工的薪水等级
select
	e.ename,
	e.sal,
	s.grade
from emp e
join salgrade s on e.sal between s.losal and s.hisal;

mysql> 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 |     1 |
| ALLEN  | 1600 |     3 |
| WARD   | 1250 |     2 |
| JONES  | 2975 |     4 |
| MARTIN | 1250 |     2 |
| BLAKE  | 2850 |     4 |
| CLARK  | 2450 |     4 |
| SCOTT  | 3000 |     4 |
| KING   | 5000 |     5 |
| TURNER | 1500 |     3 |
| ADAMS  | 1100 |     1 |
| JAMES  |  950 |     1 |
| FORD   | 3000 |     4 |
| MILLER | 1300 |     2 |
+--------+------+-------+
14 rows in set (0.00 sec)

-- 第二步：继续按照grade分组统计数量
select
	s.grade,
	count(*)
from emp e
join salgrade s on e.sal between s.losal and s.hisal
group by s.grade;

mysql> 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 |
+-------+----------+
5 rows in set (0.00 sec)

3.13、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。

3.14、列出所有员工及领导的姓名

select
	e1.ename '员工',
	e2.ename '领导'
from emp e1
join emp e2 on e1.mgr = e2.empno;

mysql> select
    -> e1.ename '员工',
    -> e2.ename '领导'
    -> from emp e1
    -> join emp e2 on e1.mgr = e2.empno;
+--------+--------+
| 员工   | 领导   |
+--------+--------+
| SMITH  | FORD   |
| ALLEN  | BLAKE  |
| WARD   | BLAKE  |
| JONES  | KING   |
| MARTIN | BLAKE  |
| BLAKE  | KING   |
| CLARK  | KING   |
| SCOTT  | JONES  |
| TURNER | BLAKE  |
| ADAMS  | SCOTT  |
| JAMES  | BLAKE  |
| FORD   | JONES  |
| MILLER | CLARK  |
+--------+--------+
13 rows in set (0.00 sec)

3.15、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

emp e1 员工表
emp e2 领导表
e1.mgr = e2.empno and e1.hiredate < e2.hiredate

select
	e1.ename '员工',
	e1.hiredate,
	e2.ename '领导',
	e2.hiredate,
	d.dname '部门名称'
from emp e1
join emp e2 on e1.mgr = e2.empno
join dept d on e1.deptno = d.deptno
where e1.hiredate < e2.hiredate;

mysql> select
    -> e1.ename '员工',
    -> e1.hiredate,
    -> e2.ename '领导',
    -> e2.hiredate,
    -> d.dname '部门名称'
    -> from emp e1
    -> join emp e2 on e1.mgr = e2.empno
    -> join dept d on e1.deptno = d.deptno
    -> where e1.hiredate < e2.hiredate;
+--------+------------+--------+------------+--------------+
| 员工   | hiredate   | 领导   | hiredate   | 部门名称     |
+--------+------------+--------+------------+--------------+
| SMITH  | 1980-12-17 | FORD   | 1981-12-03 | RESEARCH     |
| ALLEN  | 1981-02-20 | BLAKE  | 1981-05-01 | SALES        |
| WARD   | 1981-02-22 | BLAKE  | 1981-05-01 | SALES        |
| JONES  | 1981-04-02 | KING   | 1981-11-17 | RESEARCH     |
| BLAKE  | 1981-05-01 | KING   | 1981-11-17 | SALES        |
| CLARK  | 1981-06-09 | KING   | 1981-11-17 | ACCOUNTING   |
| MILLER | 1981-01-23 | CLARK  | 1981-06-09 | ACCOUNTING   |
+--------+------------+--------+------------+--------------+
7 rows in set (0.00 sec)

3.16、 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

select
	e.*,
	d.dname '部门名称'
from dept d
left join emp e on d.deptno = e.deptno;

mysql> select
    -> e.*,
    -> d.dname '部门名称'
    -> from dept d
    -> left join emp e on d.deptno = e.deptno;
+-------+--------+-----------+------+------------+------+------+--------+--------------+
| empno | ename  | job       | mgr  | hiredate   | sal  | comm | deptno | 部门名称     |
+-------+--------+-----------+------+------------+------+------+--------+--------------+
|  7369 | SMITH  | CLERK     | 7902 | 1980-12-17 |  800 | NULL |     20 | RESEARCH     |
|  7499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 | 1600 |  300 |     30 | SALES        |
|  7521 | WARD   | SALESMAN  | 7698 | 1981-02-22 | 1250 |  500 |     30 | SALES        |
|  7566 | JONES  | MANAGER   | 7839 | 1981-04-02 | 2975 | NULL |     20 | RESEARCH     |
|  7654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 | 1250 | 1400 |     30 | SALES        |
|  7698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 | 2850 | NULL |     30 | SALES        |
|  7782 | CLARK  | MANAGER   | 7839 | 1981-06-09 | 2450 | NULL |     10 | ACCOUNTING   |
|  7788 | SCOTT  | ANALYST   | 7566 | 1987-07-03 | 3000 | NULL |     20 | RESEARCH     |
|  7839 | KING   | PRESIDENT | NULL | 1981-11-17 | 5000 | NULL |     10 | ACCOUNTING   |
|  7844 | TURNER | SALESMAN  | 7698 | 1981-09-08 | 1500 |    0 |     30 | SALES        |
|  7876 | ADAMS  | CLERK     | 7788 | 1987-07-13 | 1100 | NULL |     20 | RESEARCH     |
|  7900 | JAMES  | CLERK     | 7698 | 1981-12-03 |  950 | NULL |     30 | SALES        |
|  7902 | FORD   | ANALYST   | 7566 | 1981-12-03 | 3000 | NULL |     20 | RESEARCH     |
|  7934 | MILLER | CLERK     | 7782 | 1981-01-23 | 1300 | NULL |     10 | ACCOUNTING   |
|  NULL | NULL   | NULL      | NULL | NULL       | NULL | NULL |   NULL | OPERATIONS   |
+-------+--------+-----------+------+------------+------+------+--------+--------------+
15 rows in set (0.00 sec)

3.17、列出至少有 5 个员工的所有部门

-- 每个部门的员工数量
select deptno,count(*) from emp group by deptno;

mysql> select deptno,count(*) from emp group by deptno;
+--------+----------+
| deptno | count(*) |
+--------+----------+
|     10 |        3 |
|     20 |        5 |
|     30 |        6 |
+--------+----------+
3 rows in set (0.00 sec)

-- 按照部门编号分组，计数，筛选出 >= 5
select 
	deptno,
	count(*) 
from emp 
group by deptno
having count(*) >= 5;

mysql> select 
    -> deptno,
    -> count(*) 
    -> from emp 
    -> group by deptno
    -> having count(*) >= 5;
+--------+----------+
| deptno | count(*) |
+--------+----------+
|     20 |        5 |
|     30 |        6 |
+--------+----------+
2 rows in set (0.00 sec)

3.18、列出薪金比"SMITH" 多的所有员工信息

select sal from emp where ename = 'smith';

mysql> select sal from emp where ename = 'smith';
+------+
| sal  |
+------+
|  800 |
+------+
1 row in set (0.00 sec)

select
	ename,
	sal
from emp
where sal > (select sal from emp where ename = 'smith');

mysql> select
    -> ename,
    -> sal
    -> from emp
    -> where sal > (select sal from emp where ename = 'smith');
+--------+------+
| ename  | sal  |
+--------+------+
| ALLEN  | 1600 |
| WARD   | 1250 |
| JONES  | 2975 |
| MARTIN | 1250 |
| BLAKE  | 2850 |
| CLARK  | 2450 |
| SCOTT  | 3000 |
| KING   | 5000 |
| TURNER | 1500 |
| ADAMS  | 1100 |
| JAMES  |  950 |
| FORD   | 3000 |
| MILLER | 1300 |
+--------+------+
13 rows in set (0.00 sec)

3.19、 列出所有"CLERK"( 办事员) 的姓名及其部门名称, 部门的人数

select ename,job from emp where job = 'clerk';

mysql> select ename,job from emp where job = 'clerk';
+--------+-------+
| ename  | job   |
+--------+-------+
| SMITH  | CLERK |
| ADAMS  | CLERK |
| JAMES  | CLERK |
| MILLER | CLERK |
+--------+-------+
4 rows in set (0.00 sec)

select
	e.ename,
	e.job,
	d.dname,
	d.deptno
from emp e
join dept d on e.deptno = d.deptno
where job = 'clerk';

mysql> select
    -> e.ename,
    -> e.job,
    -> d.dname,
    -> d.deptno
    -> from emp e
    -> join dept d on e.deptno = d.deptno
    -> where job = 'clerk';
+--------+-------+------------+--------+
| ename  | job   | dname      | deptno |
+--------+-------+------------+--------+
| SMITH  | CLERK | RESEARCH   |     20 |
| ADAMS  | CLERK | RESEARCH   |     20 |
| JAMES  | CLERK | SALES      |     30 |
| MILLER | CLERK | ACCOUNTING |     10 |
+--------+-------+------------+--------+
4 rows in set (0.00 sec)

select deptno,count(*) deptcount from emp group by deptno;

mysql> select deptno,count(*) deptcount from emp group by deptno;
+--------+-----------+
| deptno | deptcount |
+--------+-----------+
|     10 |         3 |
|     20 |         5 |
|     30 |         6 |
+--------+-----------+
3 rows in set (0.00 sec)

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 job = 'clerk') t1
join (select deptno,count(*) deptcount from emp group by deptno) t2 on t1.deptno = t2.deptno;

mysql> 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 job = 'clerk') t1
    -> join (select deptno,count(*) deptcount from emp group by deptno) t2 on t1.deptno = t2.deptno;
+--------+-------+------------+--------+-----------+
| ename  | job   | dname      | deptno | deptcount |
+--------+-------+------------+--------+-----------+
| SMITH  | CLERK | RESEARCH   |     20 |         5 |
| ADAMS  | CLERK | RESEARCH   |     20 |         5 |
| JAMES  | CLERK | SALES      |     30 |         6 |
| MILLER | CLERK | ACCOUNTING |     10 |         3 |
+--------+-------+------------+--------+-----------+
4 rows in set (0.00 sec)

3.20、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

select job,min(sal) from emp group by job;

mysql> select job,min(sal) from emp group by job;
+-----------+----------+
| job       | min(sal) |
+-----------+----------+
| ANALYST   |     3000 |
| CLERK     |      800 |
| MANAGER   |     2450 |
| PRESIDENT |     5000 |
| SALESMAN  |     1250 |
+-----------+----------+
5 rows in set (0.00 sec)

select job,count(*),min(sal) from emp group by job having min(sal) > 1500;

mysql> select job,count(*),min(sal) from emp group by job having min(sal) > 1500;
+-----------+----------+----------+
| job       | count(*) | min(sal) |
+-----------+----------+----------+
| ANALYST   |        2 |     3000 |
| MANAGER   |        3 |     2450 |
| PRESIDENT |        1 |     5000 |
+-----------+----------+----------+
3 rows in set (0.01 sec)

3.21、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

-- 部门编号
select deptno from dept where dname = 'sales';

mysql> select deptno from dept where dname = 'sales';
+--------+
| deptno |
+--------+
|     30 |
+--------+
1 row in set (0.00 sec)

-- 员工姓名
select ename from emp where deptno = (select deptno from dept where dname = 'sales');

mysql> select ename from emp where deptno = (select deptno from dept where dname = 'sales');
+--------+
| ename  |
+--------+
| ALLEN  |
| WARD   |
| MARTIN |
| BLAKE  |
| TURNER |
| JAMES  |
+--------+
6 rows in set (0.00 sec)

3.22、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

select avg(sal) avgsal from emp;

mysql> select avg(sal) avgsal from emp;
+-------------------+
| avgsal            |
+-------------------+
| 2073.214285714286 |
+-------------------+
1 row in set (0.00 sec)

select
	e1.ename '员工名字',
	d.dname '所在部门',
	e2.ename '上级领导',
	s.grade '工资等级'
from emp e1
left join emp e2 on e1.mgr = e2.empno
join dept d on e1.deptno = d.deptno
join salgrade s on e1.sal between s.losal and s.hisal
where e1.sal > (select avg(sal) from emp);

mysql> select
    -> e1.ename '员工名字',
    -> d.dname '所在部门',
    -> e2.ename '上级领导',
    -> s.grade '工资等级'
    -> from emp e1
    -> left join emp e2 on e1.mgr = e2.empno
    -> join dept d on e1.deptno = d.deptno
    -> join salgrade s on e1.sal between s.losal and s.hisal
    -> where e1.sal > (select avg(sal) from emp);
+--------------+--------------+--------------+--------------+
| 员工名字     | 所在部门     | 上级领导     | 工资等级     |
+--------------+--------------+--------------+--------------+
| JONES        | RESEARCH     | KING         |            4 |
| BLAKE        | SALES        | KING         |            4 |
| CLARK        | ACCOUNTING   | KING         |            4 |
| SCOTT        | RESEARCH     | JONES        |            4 |
| KING         | ACCOUNTING   | NULL         |            5 |
| FORD         | RESEARCH     | JONES        |            4 |
+--------------+--------------+--------------+--------------+
6 rows in set (0.00 sec)

3.23、 列出与"SCOTT" 从事相同工作的所有员工及部门名称

select * from emp where ename = 'scott';

mysql> select * from emp where ename = 'scott';
+-------+-------+---------+------+------------+------+------+--------+
| empno | ename | job     | mgr  | hiredate   | sal  | comm | deptno |
+-------+-------+---------+------+------------+------+------+--------+
|  7788 | SCOTT | ANALYST | 7566 | 1987-07-03 | 3000 | NULL |     20 |
+-------+-------+---------+------+------------+------+------+--------+
1 row in set (0.00 sec)

select
	e.*,
	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';

mysql> select
    -> e.*,
    -> 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';
+-------+-------+---------+------+------------+------+------+--------+----------+
| empno | ename | job     | mgr  | hiredate   | sal  | comm | deptno | dname    |
+-------+-------+---------+------+------------+------+------+--------+----------+
|  7902 | FORD  | ANALYST | 7566 | 1981-12-03 | 3000 | NULL |     20 | RESEARCH |
+-------+-------+---------+------+------------+------+------+--------+----------+
1 row in set (0.00 sec)

3.24、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

select * from emp where deptno = 30;

mysql> select * from emp where deptno = 30;
+-------+--------+----------+------+------------+------+------+--------+
| empno | ename  | job      | mgr  | hiredate   | sal  | comm | deptno |
+-------+--------+----------+------+------------+------+------+--------+
|  7499 | ALLEN  | SALESMAN | 7698 | 1981-02-20 | 1600 |  300 |     30 |
|  7521 | WARD   | SALESMAN | 7698 | 1981-02-22 | 1250 |  500 |     30 |
|  7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250 | 1400 |     30 |
|  7698 | BLAKE  | MANAGER  | 7839 | 1981-05-01 | 2850 | NULL |     30 |
|  7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500 |    0 |     30 |
|  7900 | JAMES  | CLERK    | 7698 | 1981-12-03 |  950 | NULL |     30 |
+-------+--------+----------+------+------------+------+------+--------+
6 rows in set (0.00 sec)

select distinct sal from emp where deptno = 30;

mysql> select distinct sal from emp where deptno = 30;
+------+
| sal  |
+------+
| 1600 |
| 1250 |
| 2850 |
| 1500 |
|  950 |
+------+
5 rows in set (0.00 sec)

select
	ename,
	sal
from emp
where sal in (select distinct sal from emp where deptno = 30)
and deptno <> 30;

mysql> select
    -> ename,
    -> sal
    -> from emp
    -> where sal in (select distinct sal from emp where deptno = 30)
    -> and deptno <> 30;
Empty set (0.00 sec)

3.25、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

select max(sal) from emp where deptno = 30;

mysql> select max(sal) from emp where deptno = 30;
+----------+
| max(sal) |
+----------+
|     2850 |
+----------+
1 row in set (0.00 sec)

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);

mysql> 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      |
+-------+------+------------+
| JONES | 2975 | RESEARCH   |
| SCOTT | 3000 | RESEARCH   |
| KING  | 5000 | ACCOUNTING |
| FORD  | 3000 | RESEARCH   |
+-------+------+------------+
4 rows in set (0.00 sec)

3.26、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

select
	d.deptno,
	count(e.ename),
	ifnull(avg(e.sal),0) as avgsal,
	ifnull(avg(timestampdiff(YEAR, hiredate, now())), 0) as avgservicetime
from dept d
left join emp e on d.deptno = e.deptno
group by d.deptno;

mysql> select
    -> d.deptno,
    -> count(e.ename),
    -> ifnull(avg(e.sal),0) as avgsal,
    -> ifnull(avg(timestampdiff(YEAR, hiredate, now())), 0) as avgservicetime
    -> from dept d
    -> left join emp e on d.deptno = e.deptno
    -> group by d.deptno;
+--------+----------------+--------------------+----------------+
| deptno | count(e.ename) | avgsal             | avgservicetime |
+--------+----------------+--------------------+----------------+
|     10 |              3 | 2916.6666666666665 |        42.3333 |
|     20 |              5 |               2175 |        39.8000 |
|     30 |              6 | 1566.6666666666667 |        42.0000 |
|     40 |              0 |                  0 |         0.0000 |
+--------+----------------+--------------------+----------------+
4 rows in set (0.00 sec)

3.26、在mysql当中怎么计算两个日期的“年差”，差了多少年【知识点】

TimeStampDiff(间隔类型, 前一个日期, 后一个日期)
	
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

3.27、 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
join dept d on e.deptno = d.deptno
order by e.sal desc;

mysql> select
    -> e.ename,
    -> d.dname,
    -> e.sal
    -> from emp e
    -> join dept d on e.deptno = d.deptno
    -> order by e.sal desc;
+--------+------------+------+
| ename  | dname      | sal  |
+--------+------------+------+
| KING   | ACCOUNTING | 5000 |
| SCOTT  | RESEARCH   | 3000 |
| FORD   | RESEARCH   | 3000 |
| JONES  | RESEARCH   | 2975 |
| BLAKE  | SALES      | 2850 |
| CLARK  | ACCOUNTING | 2450 |
| ALLEN  | SALES      | 1600 |
| TURNER | SALES      | 1500 |
| MILLER | ACCOUNTING | 1300 |
| MARTIN | SALES      | 1250 |
| WARD   | SALES      | 1250 |
| ADAMS  | RESEARCH   | 1100 |
| JAMES  | SALES      |  950 |
| SMITH  | RESEARCH   |  800 |
+--------+------------+------+
14 rows in set (0.00 sec)

3.28、列出所有部门的详细信息和人数

select
	d.*,
	count(e.ename)
from dept d
left join emp e on d.deptno = e.deptno
group by d.deptno;

mysql> select
    -> d.*,
    -> count(e.ename)
    -> from dept d
    -> left join emp e on d.deptno = e.deptno
    -> group by d.deptno;
+--------+------------+----------+----------------+
| deptno | dname      | loc      | count(e.ename) |
+--------+------------+----------+----------------+
|     10 | ACCOUNTING | NEW YORK |              3 |
|     20 | RESEARCH   | DALLAS   |              5 |
|     30 | SALES      | CHICAGO  |              6 |
|     40 | OPERATIONS | BOSTON   |              0 |
+--------+------------+----------+----------------+
4 rows in set (0.00 sec)

3.29、列出各种工作的最低工资及从事此工作的雇员姓名

select job,min(sal) from emp group by job;

mysql> select job,min(sal) from emp group by job;
+-----------+----------+
| job       | min(sal) |
+-----------+----------+
| ANALYST   |     3000 |
| CLERK     |      800 |
| MANAGER   |     2450 |
| PRESIDENT |     5000 |
| SALESMAN  |     1250 |
+-----------+----------+
5 rows in set (0.00 sec)

select
	e.ename,
	t.job,
	t.minsal
from emp e
join (select job,min(sal) minsal from emp group by job) t 
on e.job = t.job and e.sal = t.minsal;

mysql> select
    -> e.ename,
    -> t.job,
    -> t.minsal
    -> from emp e
    -> join (select job,min(sal) minsal from emp group by job) t 
    -> on e.job = t.job and e.sal = t.minsal;
+--------+-----------+--------+
| ename  | job       | minsal |
+--------+-----------+--------+
| SMITH  | CLERK     |    800 |
| WARD   | SALESMAN  |   1250 |
| MARTIN | SALESMAN  |   1250 |
| CLARK  | MANAGER   |   2450 |
| SCOTT  | ANALYST   |   3000 |
| KING   | PRESIDENT |   5000 |
| FORD   | ANALYST   |   3000 |
+--------+-----------+--------+
7 rows in set (0.00 sec)

3.30、列出各个部门的 MANAGER( 领导) 的最低薪金

select
	deptno,
	min(sal)
from emp
where job = 'manager'
group by deptno;

mysql> select
    -> deptno,
    -> min(sal)
    -> from emp
    -> where job = 'manager'
    -> group by deptno;
+--------+----------+
| deptno | min(sal) |
+--------+----------+
|     10 |     2450 |
|     20 |     2975 |
|     30 |     2850 |
+--------+----------+
3 rows in set (0.00 sec)

3.31、列出所有员工的 年工资, 按 年薪从低到高排序

select
	ename,
	(sal + ifnull(comm,0) ) * 12 yearsal
from emp
order by yearsal asc;

mysql> select
    -> ename,
    -> (sal + ifnull(comm,0) ) * 12 yearsal
    -> from emp
    -> order by yearsal asc;
+--------+---------+
| ename  | yearsal |
+--------+---------+
| SMITH  |    9600 |
| JAMES  |   11400 |
| ADAMS  |   13200 |
| MILLER |   15600 |
| TURNER |   18000 |
| WARD   |   21000 |
| ALLEN  |   22800 |
| CLARK  |   29400 |
| MARTIN |   31800 |
| BLAKE  |   34200 |
| JONES  |   35700 |
| SCOTT  |   36000 |
| FORD   |   36000 |
| KING   |   60000 |
+--------+---------+
14 rows in set (0.01 sec)

3.32、求出员工领导的薪水超过3000的员工名称与领导

select
	e1.ename '员工',
	e1.sal '员工薪水',
	e2.ename '领导',
	e2.sal '领导薪水'
from emp e1
join emp e2 on e1.mgr = e2.empno
where e2.sal > 3000;

mysql> select
    -> e1.ename '员工',
    -> e1.sal '员工薪水',
    -> e2.ename '领导',
    -> e2.sal '领导薪水'
    -> from emp e1
    -> join emp e2 on e1.mgr = e2.empno
    -> where e2.sal > 3000;
+--------+--------------+--------+--------------+
| 员工   | 员工薪水     | 领导   | 领导薪水     |
+--------+--------------+--------+--------------+
| JONES  |         2975 | KING   |         5000 |
| BLAKE  |         2850 | KING   |         5000 |
| CLARK  |         2450 | KING   |         5000 |
+--------+--------------+--------+--------------+
3 rows in set (0.00 sec)

3.33、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

select
	d.*,
	count(e.ename),
	ifnull(sum(e.sal),0) sumsal
from dept d
left join emp e on d.deptno = e.deptno
where d.dname like '%s%'
group by d.deptno;

mysql> select
    -> d.*,
    -> count(e.ename),
    -> ifnull(sum(e.sal),0) sumsal
    -> from dept d
    -> left join emp e on d.deptno = e.deptno
    -> where d.dname like '%s%'
    -> group by d.deptno;
+--------+------------+---------+----------------+--------+
| deptno | dname      | loc     | count(e.ename) | sumsal |
+--------+------------+---------+----------------+--------+
|     20 | RESEARCH   | DALLAS  |              5 |  10875 |
|     30 | SALES      | CHICAGO |              6 |   9400 |
|     40 | OPERATIONS | BOSTON  |              0 |      0 |
+--------+------------+---------+----------------+--------+
3 rows in set (0.00 sec)

3.34、给任职日期超过 30 年的员工加薪 10%

-- 复制一张表
create table emp_bak as select * from emp;

mysql> create table emp_bak as select * from emp;
Query OK, 14 rows affected (0.01 sec)
Records: 14  Duplicates: 0  Warnings: 0

mysql> select * from emp_bak;
+-------+--------+-----------+------+------------+------+------+--------+
| empno | ename  | job       | mgr  | hiredate   | sal  | comm | deptno |
+-------+--------+-----------+------+------------+------+------+--------+
|  7369 | SMITH  | CLERK     | 7902 | 1980-12-17 |  800 | NULL |     20 |
|  7499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 | 1600 |  300 |     30 |
|  7521 | WARD   | SALESMAN  | 7698 | 1981-02-22 | 1250 |  500 |     30 |
|  7566 | JONES  | MANAGER   | 7839 | 1981-04-02 | 2975 | NULL |     20 |
|  7654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 | 1250 | 1400 |     30 |
|  7698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 | 2850 | NULL |     30 |
|  7782 | CLARK  | MANAGER   | 7839 | 1981-06-09 | 2450 | NULL |     10 |
|  7788 | SCOTT  | ANALYST   | 7566 | 1987-07-03 | 3000 | NULL |     20 |
|  7839 | KING   | PRESIDENT | NULL | 1981-11-17 | 5000 | NULL |     10 |
|  7844 | TURNER | SALESMAN  | 7698 | 1981-09-08 | 1500 |    0 |     30 |
|  7876 | ADAMS  | CLERK     | 7788 | 1987-07-13 | 1100 | NULL |     20 |
|  7900 | JAMES  | CLERK     | 7698 | 1981-12-03 |  950 | NULL |     30 |
|  7902 | FORD   | ANALYST   | 7566 | 1981-12-03 | 3000 | NULL |     20 |
|  7934 | MILLER | CLERK     | 7782 | 1981-01-23 | 1300 | NULL |     10 |
+-------+--------+-----------+------+------------+------+------+--------+
14 rows in set (0.00 sec)

-- 更新表
update emp set sal = sal * 1.1 where timestampdiff(YEAR, hiredate, now()) > 30;

mysql> update emp set sal = sal * 1.1 where timestampdiff(YEAR, hiredate, now()) > 30;
Query OK, 14 rows affected (0.01 sec)
Rows matched: 14  Changed: 14  Warnings: 0

mysql> select * from emp;
+-------+--------+-----------+------+------------+--------------------+------+--------+
| empno | ename  | job       | mgr  | hiredate   | sal                | comm | deptno |
+-------+--------+-----------+------+------------+--------------------+------+--------+
|  7369 | SMITH  | CLERK     | 7902 | 1980-12-17 |  880.0000000000001 | NULL |     20 |
|  7499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 | 1760.0000000000002 |  300 |     30 |
|  7521 | WARD   | SALESMAN  | 7698 | 1981-02-22 |               1375 |  500 |     30 |
|  7566 | JONES  | MANAGER   | 7839 | 1981-04-02 | 3272.5000000000005 | NULL |     20 |
|  7654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 |               1375 | 1400 |     30 |
|  7698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 | 3135.0000000000005 | NULL |     30 |
|  7782 | CLARK  | MANAGER   | 7839 | 1981-06-09 |               2695 | NULL |     10 |
|  7788 | SCOTT  | ANALYST   | 7566 | 1987-07-03 | 3300.0000000000005 | NULL |     20 |
|  7839 | KING   | PRESIDENT | NULL | 1981-11-17 |               5500 | NULL |     10 |
|  7844 | TURNER | SALESMAN  | 7698 | 1981-09-08 | 1650.0000000000002 |    0 |     30 |
|  7876 | ADAMS  | CLERK     | 7788 | 1987-07-13 |               1210 | NULL |     20 |
|  7900 | JAMES  | CLERK     | 7698 | 1981-12-03 |               1045 | NULL |     30 |
|  7902 | FORD   | ANALYST   | 7566 | 1981-12-03 | 3300.0000000000005 | NULL |     20 |
|  7934 | MILLER | CLERK     | 7782 | 1981-01-23 | 1430.0000000000002 | NULL |     10 |
+-------+--------+-----------+------+------------+--------------------+------+--------+
14 rows in set (0.00 sec)

endl