MySQL 复合查询

目录

[1. 基本查询回顾](#1. 基本查询回顾)

[2. 多表查询](#2. 多表查询)

[3. 自连接](#3. 自连接)

[4. 子查寻](#4. 子查寻)

[4.1 单行子查询](#4.1 单行子查询)

[4.2 多行子查询](#4.2 多行子查询)

[4.3 多列子查询](#4.3 多列子查询)

[4.4 在from子句中使用子查询](#4.4 在from子句中使用子查询)

[4.5 合并查询](#4.5 合并查询)

[4.5.1 union](#4.5.1 union)

[4.5.2 union all](#4.5.2 union all)

---

正文开始：

1. 基本查询回顾

mysql> show tables;
+---------------+
| Tables_in_db5 |
+---------------+
| DEPT          |
| EMP           |
| SALGRADE      |
+---------------+
3 rows in set (0.00 sec)

mysql> select * from DEPT;
+--------+------------+----------+
| DEPTNO | DNAME      | LOC      |
+--------+------------+----------+
|     10 | ACCOUNTING | NEW YORK |
|     20 | RESEARCH   | DALLAS   |
|     30 | SALES      | CHICAGO  |
|     40 | OPERATIONS | BOSTON   |
+--------+------------+----------+
4 rows in set (0.01 sec)

mysql> select * from EMP;
+-------+--------+-----------+------+------------+---------+---------+--------+
| EMPNO | ENAME  | JOB       | MGR  | HIREDATE   | SAL     | COMM    | DEPTNO |
+-------+--------+-----------+------+------------+---------+---------+--------+
|  7369 | SMITH  | CLERK     | 7902 | 1980-12-17 |  800.00 |    NULL |     20 |
|  7499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 | 1600.00 |  300.00 |     30 |
|  7521 | WARD   | SALESMAN  | 7698 | 1981-02-22 | 1250.00 |  500.00 |     30 |
|  7566 | JONES  | MANAGER   | 7839 | 1981-04-02 | 2975.00 |    NULL |     20 |
|  7654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 | 1250.00 | 1400.00 |     30 |
|  7698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 | 2850.00 |    NULL |     30 |
|  7782 | CLARK  | MANAGER   | 7839 | 1981-06-09 | 2450.00 |    NULL |     10 |
|  7788 | SCOTT  | ANALYST   | 7566 | 1982-12-09 | 3000.00 |    NULL |     20 |
|  7839 | KING   | PRESIDENT | NULL | 1981-11-17 | 5000.00 |    NULL |     10 |
|  7844 | TURNER | SALESMAN  | 7698 | 1981-09-08 | 1500.00 |    0.00 |     30 |
|  7876 | ADAMS  | CLERK     | 7788 | 1983-01-12 | 1100.00 |    NULL |     20 |
|  7900 | JAMES  | CLERK     | 7698 | 1981-12-03 |  950.00 |    NULL |     30 |
|  7902 | FORD   | ANALYST   | 7566 | 1981-12-03 | 3000.00 |    NULL |     20 |
|  7934 | MILLER | CLERK     | 7782 | 1982-01-23 | 1300.00 |    NULL |     10 |
+-------+--------+-----------+------+------------+---------+---------+--------+
14 rows in set (0.00 sec)

mysql> select * from SALGRADE;
+-------+-------+-------+
| GRADE | LOSAL | HISAL |
+-------+-------+-------+
|     1 |   700 |  1200 |
|     2 |  1201 |  1400 |
|     3 |  1401 |  2000 |
|     4 |  2001 |  3000 |
|     5 |  3001 |  9999 |
+-------+-------+-------+
5 rows in set (0.00 sec)

1. 查询工资高于500或岗位为MANAGER的雇员，同时还要满足他们的姓名首字母为大写的J

mysql> select * from EMP where (sal > 500 or job='MANAGER') and ename like 'J%';
+-------+-------+---------+------+------------+---------+------+--------+
| EMPNO | ENAME | JOB     | MGR  | HIREDATE   | SAL     | COMM | DEPTNO |
+-------+-------+---------+------+------------+---------+------+--------+
|  7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | NULL |     20 |
|  7900 | JAMES | CLERK   | 7698 | 1981-12-03 |  950.00 | NULL |     30 |
+-------+-------+---------+------+------------+---------+------+--------+
2 rows in set (0.00 sec)

2. 按照部门号升序而雇员的工资降序排序

mysql> select * from EMP order by deptno, sal desc;
+-------+--------+-----------+------+------------+---------+---------+--------+
| EMPNO | ENAME  | JOB       | MGR  | HIREDATE   | SAL     | COMM    | DEPTNO |
+-------+--------+-----------+------+------------+---------+---------+--------+
|  7839 | KING   | PRESIDENT | NULL | 1981-11-17 | 5000.00 |    NULL |     10 |
|  7782 | CLARK  | MANAGER   | 7839 | 1981-06-09 | 2450.00 |    NULL |     10 |
|  7934 | MILLER | CLERK     | 7782 | 1982-01-23 | 1300.00 |    NULL |     10 |
|  7788 | SCOTT  | ANALYST   | 7566 | 1982-12-09 | 3000.00 |    NULL |     20 |
|  7902 | FORD   | ANALYST   | 7566 | 1981-12-03 | 3000.00 |    NULL |     20 |
|  7566 | JONES  | MANAGER   | 7839 | 1981-04-02 | 2975.00 |    NULL |     20 |
|  7876 | ADAMS  | CLERK     | 7788 | 1983-01-12 | 1100.00 |    NULL |     20 |
|  7369 | SMITH  | CLERK     | 7902 | 1980-12-17 |  800.00 |    NULL |     20 |
|  7698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 | 2850.00 |    NULL |     30 |
|  7499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 | 1600.00 |  300.00 |     30 |
|  7844 | TURNER | SALESMAN  | 7698 | 1981-09-08 | 1500.00 |    0.00 |     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 |
|  7900 | JAMES  | CLERK     | 7698 | 1981-12-03 |  950.00 |    NULL |     30 |
+-------+--------+-----------+------+------------+---------+---------+--------+
14 rows in set (0.00 sec)

3. 使用年薪进行降序排序

mysql> select ename, sal*12+ifnull(comm, 0) as '年薪' from EMP order by 年薪 desc;
+--------+----------+
| ename  | 年薪     |
+--------+----------+
| KING   | 60000.00 |
| SCOTT  | 36000.00 |
| FORD   | 36000.00 |
| JONES  | 35700.00 |
| BLAKE  | 34200.00 |
| CLARK  | 29400.00 |
| ALLEN  | 19500.00 |
| TURNER | 18000.00 |
| MARTIN | 16400.00 |
| MILLER | 15600.00 |
| WARD   | 15500.00 |
| ADAMS  | 13200.00 |
| JAMES  | 11400.00 |
| SMITH  |  9600.00 |
+--------+----------+
14 rows in set (0.00 sec)

4. 显示工资最高的员工的名字和工作岗位

mysql> select ename, job from EMP where sal = (select max(sal) from EMP);
+-------+-----------+
| ename | job       |
+-------+-----------+
| KING  | PRESIDENT |
+-------+-----------+
1 row in set (0.00 sec)

5. 显示工资高于平均工资的员工信息

mysql> select ename, sal from EMP where sal > (select avg(sal) from EMP);
+-------+---------+
| ename | sal     |
+-------+---------+
| JONES | 2975.00 |
| BLAKE | 2850.00 |
| CLARK | 2450.00 |
| SCOTT | 3000.00 |
| KING  | 5000.00 |
| FORD  | 3000.00 |
+-------+---------+
6 rows in set (0.00 sec)

6. 显示每个部门的平均工资和最高工资

mysql> select deptno, format(avg(sal), 2), max(sal) from EMP group by deptno;
+--------+---------------------+----------+
| deptno | format(avg(sal), 2) | max(sal) |
+--------+---------------------+----------+
|     10 | 2,916.67            |  5000.00 |
|     20 | 2,175.00            |  3000.00 |
|     30 | 1,566.67            |  2850.00 |
+--------+---------------------+----------+
3 rows in set (0.00 sec)

7. 显示平均工资低于2000的部门号和它的平均工资

mysql> select deptno, avg(sal) as avg_sal from EMP group by deptno having avg_sal < 2000;
+--------+-------------+
| deptno | avg_sal     |
+--------+-------------+
|     30 | 1566.666667 |
+--------+-------------+
1 row in set (0.00 sec)

8. 显示每种岗位的雇员总数，平均工资

mysql> select job, count(*), format(avg(sal), 2) from EMP group by job;
+-----------+----------+---------------------+
| job       | count(*) | format(avg(sal), 2) |
+-----------+----------+---------------------+
| CLERK     |        4 | 1,037.50            |
| SALESMAN  |        4 | 1,400.00            |
| MANAGER   |        3 | 2,758.33            |
| ANALYST   |        2 | 3,000.00            |
| PRESIDENT |        1 | 5,000.00            |
+-----------+----------+---------------------+
5 rows in set (0.00 sec)

2. 多表查询

实际开发中往往数据来自不同的表，所以需要多表查询。本节我们用一个简单的公司管理系统，有三张表EMP,DEPT,SALGRADE来演示如何进行多表查询（三表中内容可见文章开头）。

案例：

1. 显示雇员名、雇员工资以及所在部门的名字因为上面的数据来自EMP和DEPT表，因此要联合查询

其实我们只要emp表中的deptno = dept表中的deptno字段的记录

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

2. 显示部门号为10的部门名，员工名和工资

mysql> select ename, sal, dname from EMP, DEPT where EMP.deptno=DEPT.deptno and DEPT.deptno = 10;
+--------+---------+------------+
| ename  | sal     | dname      |
+--------+---------+------------+
| CLARK  | 2450.00 | ACCOUNTING |
| KING   | 5000.00 | ACCOUNTING |
| MILLER | 1300.00 | ACCOUNTING |
+--------+---------+------------+
3 rows in set (0.00 sec)

3. 显示各个员工的姓名，工资，及工资级别

mysql> select ename, sal, grade from EMP, SALGRADE where EMP.sal between losal and 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)

3. 自连接

自连接是指在同一张表连接查询

案例：

显示员工FORD的上级领导的编号和姓名（mgr是员工领导的编号--empno）

1. 使用的子查询：

mysql> select empno, ename from EMP where EMP.empno=(select mgr from EMP where ename='FORD');
+-------+-------+
| empno | ename |
+-------+-------+
|  7566 | JONES |
+-------+-------+
1 row in set (0.00 sec)

2. 使用多表查询（自查询）

-- 使用到表的别名
--from emp leader, emp worker，给自己的表起别名，因为要先做笛卡尔积，所以别名可以先识别

mysql> select leader.empno, leader.ename from EMP leader, EMP worker where leader.empno=worker.mgr and worker.ename='FORD';
+-------+-------+
| empno | ename |
+-------+-------+
|  7566 | JONES |
+-------+-------+
1 row in set (0.00 sec)

4. 子查寻

子查询是指嵌入在其他sql语句中的select语句，也叫嵌套查询

4.1 单行子查询

返回一行记录的子查询

1. 显示SMITH同一个部门的员工

mysql> select * from EMP where deptno=(select deptno from EMP where ename='smith');
+-------+-------+---------+------+------------+---------+------+--------+
| EMPNO | ENAME | JOB     | MGR  | HIREDATE   | SAL     | COMM | DEPTNO |
+-------+-------+---------+------+------------+---------+------+--------+
|  7369 | SMITH | CLERK   | 7902 | 1980-12-17 |  800.00 | NULL |     20 |
|  7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | NULL |     20 |
|  7788 | SCOTT | ANALYST | 7566 | 1982-12-09 | 3000.00 | NULL |     20 |
|  7876 | ADAMS | CLERK   | 7788 | 1983-01-12 | 1100.00 | NULL |     20 |
|  7902 | FORD  | ANALYST | 7566 | 1981-12-03 | 3000.00 | NULL |     20 |
+-------+-------+---------+------+------------+---------+------+--------+
5 rows in set (0.00 sec)

4.2 多行子查询

返回多行记录的子查询

1. in关键字； 查询和10号部门的工作岗位相同的雇员的名字，岗位，工资，部门号，但是不包含10自己的

mysql> select ename,job,sal,deptno from EMP where job in (select distinct job from EMP where deptno=10) and deptno<>10;
+-------+---------+---------+--------+
| ename | job     | sal     | deptno |
+-------+---------+---------+--------+
| SMITH | CLERK   |  800.00 |     20 |
| JONES | MANAGER | 2975.00 |     20 |
| BLAKE | MANAGER | 2850.00 |     30 |
| ADAMS | CLERK   | 1100.00 |     20 |
| JAMES | CLERK   |  950.00 |     30 |
+-------+---------+---------+--------+
5 rows in set (0.00 sec)

2. all关键字； 显示工资比部门30的所有员工的工资高的员工的姓名、工资和部门号

mysql> select ename,sal,deptno from EMP where sal > all(select sal from EMP where deptno=30);
+-------+---------+--------+
| ename | sal     | deptno |
+-------+---------+--------+
| JONES | 2975.00 |     20 |
| SCOTT | 3000.00 |     20 |
| KING  | 5000.00 |     10 |
| FORD  | 3000.00 |     20 |
+-------+---------+--------+
4 rows in set (0.00 sec)

3. any关键字； 显示工资比部门30的任意员工的工资高的员工的姓名、工资和部门号（包含自己部门的员工）

mysql> select ename,sal,deptno from EMP where sal > any(select sal from EMP where deptno=30);
+--------+---------+--------+
| ename  | sal     | deptno |
+--------+---------+--------+
| ALLEN  | 1600.00 |     30 |
| WARD   | 1250.00 |     30 |
| JONES  | 2975.00 |     20 |
| MARTIN | 1250.00 |     30 |
| BLAKE  | 2850.00 |     30 |
| CLARK  | 2450.00 |     10 |
| SCOTT  | 3000.00 |     20 |
| KING   | 5000.00 |     10 |
| TURNER | 1500.00 |     30 |
| ADAMS  | 1100.00 |     20 |
| FORD   | 3000.00 |     20 |
| MILLER | 1300.00 |     10 |
+--------+---------+--------+
12 rows in set (0.00 sec)

4.3 多列子查询

单行子查询是指子查询只返回单列，单行数据；多行子查询是指返回单列多行数据，都是针对单列而言的，而多列子查询则是指查询返回多个列数据的子查询语句

案例：查询和SMITH的部门和岗位完全相同的所有雇员，不含SMITH本人

mysql> select ename from EMP where (deptno,job)=(select deptno,job from EMP where ename='SMITH') and ename<>'SMITH';
+-------+
| ename |
+-------+
| ADAMS |
+-------+
1 row in set (0.00 sec)

4.4 在from子句中使用子查询

子查询语句出现在from子句中。这里要用到数据查询的技巧，把一个子查询当做一个临时表使用。

示例：

1. 显示每个高于自己部门平均工资的员工的姓名、部门、工资、平均工资

--获取各个部门的平均工资，将其看作临时表

mysql> select ename,deptno,sal,format(asal, 2) from EMP,
    -> (select avg(sal) asal, deptno dt from EMP group by deptno) tmp
    -> where EMP.sal > tmp.asal and EMP.deptno=tmp.dt;
+-------+--------+---------+-----------------+
| ename | deptno | sal     | format(asal, 2) |
+-------+--------+---------+-----------------+
| KING  |     10 | 5000.00 | 2,916.67        |
| JONES |     20 | 2975.00 | 2,175.00        |
| SCOTT |     20 | 3000.00 | 2,175.00        |
| FORD  |     20 | 3000.00 | 2,175.00        |
| ALLEN |     30 | 1600.00 | 1,566.67        |
| BLAKE |     30 | 2850.00 | 1,566.67        |
+-------+--------+---------+-----------------+
6 rows in set (0.00 sec)

2. 查找每个部门工资最高的人的姓名、工资、部门、最高工资

mysql> select EMP.ename, EMP.sal, EMP.deptno, ms from EMP,
    -> (select max(sal) ms, deptno from EMP group by deptno) tmp
    -> where EMP.deptno=tmp.deptno and EMP.sal=tmp.ms;
+-------+---------+--------+---------+
| ename | sal     | deptno | ms      |
+-------+---------+--------+---------+
| BLAKE | 2850.00 |     30 | 2850.00 |
| SCOTT | 3000.00 |     20 | 3000.00 |
| KING  | 5000.00 |     10 | 5000.00 |
| FORD  | 3000.00 |     20 | 3000.00 |
+-------+---------+--------+---------+
4 rows in set (0.00 sec)

3. 显示每个部门的信息（部门名，编号，地址）和人员数量

--方法一：使用多表
mysql> select DEPT.dname, DEPT.deptno, DEPT.loc,count(*) '部门人数' from EMP,DEPT
    -> where EMP.deptno=DEPT.deptno
    -> group by DEPT.deptno,DEPT.dname,DEPT.loc;
+------------+--------+----------+--------------+
| dname      | deptno | loc      | 部门人数     |
+------------+--------+----------+--------------+
| ACCOUNTING |     10 | NEW YORK |            3 |
| RESEARCH   |     20 | DALLAS   |            5 |
| SALES      |     30 | CHICAGO  |            6 |
+------------+--------+----------+--------------+
3 rows in set (0.00 sec)



--方法二：使用子查询
-- 1. 对EMP表进行人员统计
mysql> select count(*), deptno from EMP group by deptno;
+----------+--------+
| count(*) | deptno |
+----------+--------+
|        3 |     10 |
|        5 |     20 |
|        6 |     30 |
+----------+--------+
3 rows in set (0.00 sec)
-- 2. 将上面的表看作临时表
mysql> select DEPT.deptno, dname, mycnt, loc from DEPT,
    -> (select count(*) mycnt, deptno from EMP group by deptno) tmp
    -> where DEPT.deptno=tmp.deptno;
+--------+------------+-------+----------+
| deptno | dname      | mycnt | loc      |
+--------+------------+-------+----------+
|     10 | ACCOUNTING |     3 | NEW YORK |
|     20 | RESEARCH   |     5 | DALLAS   |
|     30 | SALES      |     6 | CHICAGO  |
+--------+------------+-------+----------+
3 rows in set (0.00 sec)

4.5 合并查询

在实际应用中，为了合并多个select的执行结果，可以使用集合操作符 union，union all

4.5.1 union

该操作符用于取得两个结果集的并集。当使用该操作符时，会自动去掉结果集中的重复行。

案例：将工资大于2500或职位是MANAGER的人找出来

mysql> select ename, sal, job from EMP where sal>2500 
    -> union select ename, sal, job from EMP where job='MANAGER';--去掉了重复记录
+-------+---------+-----------+
| ename | sal     | job       |
+-------+---------+-----------+
| JONES | 2975.00 | MANAGER   |
| BLAKE | 2850.00 | MANAGER   |
| SCOTT | 3000.00 | ANALYST   |
| KING  | 5000.00 | PRESIDENT |
| FORD  | 3000.00 | ANALYST   |
| CLARK | 2450.00 | MANAGER   |
+-------+---------+-----------+
6 rows in set (0.00 sec)

4.5.2 union all

该操作符用于取得两个结果集的并集。当使用该操作符时，不会去掉结果集中的重复行。

案例：将工资大于25000或职位是MANAGER的人找出来

mysql> select ename, sal, job from EMP where sal>2500
    -> union all select ename, sal, job from EMP where job='MANAGER';
+-------+---------+-----------+
| ename | sal     | job       |
+-------+---------+-----------+
| JONES | 2975.00 | MANAGER   |
| BLAKE | 2850.00 | MANAGER   |
| SCOTT | 3000.00 | ANALYST   |
| KING  | 5000.00 | PRESIDENT |
| FORD  | 3000.00 | ANALYST   |
| JONES | 2975.00 | MANAGER   |
| BLAKE | 2850.00 | MANAGER   |
| CLARK | 2450.00 | MANAGER   |
+-------+---------+-----------+
8 rows in set (0.00 sec)