【MySQL-6】MySQL的复合查询

1. 整体学习的思维导图

2. 回顾基本查询

3. 多表查询

4. 自连接

5. 子查询

5.1 单行子查询

5.2 多行子查询

5.3 多列子查询

5.4 在from子句中使用子查询

6. 合并查询

1. 整体学习的思维导图

2. 回顾基本查询

使用scott数据库中的表，完成以下查询：

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 |
+--------+-------+---------+------+---------------------+---------+------+--------+
| 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL |     20 |
| 007900 | JAMES | CLERK   | 7698 | 1981-12-03 00:00:00 |  950.00 | NULL |     30 |
+--------+-------+---------+------+---------------------+---------+------+--------+

按照部门号升序而雇员的工资降序排序

mysql> select * from emp order by deptno asc, sal desc;
+--------+--------+-----------+------+---------------------+---------+---------+--------+
| empno  | ename  | job       | mgr  | hiredate            | sal     | comm    | deptno |
+--------+--------+-----------+------+---------------------+---------+---------+--------+
| 007839 | KING   | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 |    NULL |     10 |
| 007782 | CLARK  | MANAGER   | 7839 | 1981-06-09 00:00:00 | 2450.00 |    NULL |     10 |
| 007934 | MILLER | CLERK     | 7782 | 1982-01-23 00:00:00 | 1300.00 |    NULL |     10 |
| 007788 | SCOTT  | ANALYST   | 7566 | 1987-04-19 00:00:00 | 3000.00 |    NULL |     20 |
| 007902 | FORD   | ANALYST   | 7566 | 1981-12-03 00:00:00 | 3000.00 |    NULL |     20 |
| 007566 | JONES  | MANAGER   | 7839 | 1981-04-02 00:00:00 | 2975.00 |    NULL |     20 |
| 007876 | ADAMS  | CLERK     | 7788 | 1987-05-23 00:00:00 | 1100.00 |    NULL |     20 |
| 007369 | SMITH  | CLERK     | 7902 | 1980-12-17 00:00:00 |  800.00 |    NULL |     20 |
| 007698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 00:00:00 | 2850.00 |    NULL |     30 |
| 007499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 00:00:00 | 1600.00 |  300.00 |     30 |
| 007844 | TURNER | SALESMAN  | 7698 | 1981-09-08 00:00:00 | 1500.00 |    0.00 |     30 |
| 007521 | WARD   | SALESMAN  | 7698 | 1981-02-22 00:00:00 | 1250.00 |  500.00 |     30 |
| 007654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 |     30 |
| 007900 | JAMES  | CLERK     | 7698 | 1981-12-03 00:00:00 |  950.00 |    NULL |     30 |
+--------+--------+-----------+------+---------------------+---------+---------+--------+

使用年薪进行降序排序

mysql> select *,sal*12+ifnull(comm,0) 年薪 from emp order by 年薪 desc;
+--------+--------+-----------+------+---------------------+---------+---------+--------+----------+
| empno  | ename  | job       | mgr  | hiredate            | sal     | comm    | deptno | 年薪     |
+--------+--------+-----------+------+---------------------+---------+---------+--------+----------+
| 007839 | KING   | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 |    NULL |     10 | 60000.00 |
| 007788 | SCOTT  | ANALYST   | 7566 | 1987-04-19 00:00:00 | 3000.00 |    NULL |     20 | 36000.00 |
| 007902 | FORD   | ANALYST   | 7566 | 1981-12-03 00:00:00 | 3000.00 |    NULL |     20 | 36000.00 |
| 007566 | JONES  | MANAGER   | 7839 | 1981-04-02 00:00:00 | 2975.00 |    NULL |     20 | 35700.00 |
| 007698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 00:00:00 | 2850.00 |    NULL |     30 | 34200.00 |
| 007782 | CLARK  | MANAGER   | 7839 | 1981-06-09 00:00:00 | 2450.00 |    NULL |     10 | 29400.00 |
| 007499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 00:00:00 | 1600.00 |  300.00 |     30 | 19500.00 |
| 007844 | TURNER | SALESMAN  | 7698 | 1981-09-08 00:00:00 | 1500.00 |    0.00 |     30 | 18000.00 |
| 007654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 |     30 | 16400.00 |
| 007934 | MILLER | CLERK     | 7782 | 1982-01-23 00:00:00 | 1300.00 |    NULL |     10 | 15600.00 |
| 007521 | WARD   | SALESMAN  | 7698 | 1981-02-22 00:00:00 | 1250.00 |  500.00 |     30 | 15500.00 |
| 007876 | ADAMS  | CLERK     | 7788 | 1987-05-23 00:00:00 | 1100.00 |    NULL |     20 | 13200.00 |
| 007900 | JAMES  | CLERK     | 7698 | 1981-12-03 00:00:00 |  950.00 |    NULL |     30 | 11400.00 |
| 007369 | SMITH  | CLERK     | 7902 | 1980-12-17 00:00:00 |  800.00 |    NULL |     20 |  9600.00 |
+--------+--------+-----------+------+---------------------+---------+---------+--------+----------+

显示工资最高的员工的名字和工作岗位

mysql> select ename,job,sal from emp where sal=(select max(sal) from emp);
+-------+-----------+---------+
| ename | job       | sal     |
+-------+-----------+---------+
| KING  | PRESIDENT | 5000.00 |
+-------+-----------+---------+

显示工资高于平均工资的员工信息

mysql> select * from emp where sal>(select avg(sal) mysal from emp);
+--------+-------+-----------+------+---------------------+---------+------+--------+
| empno  | ename | job       | mgr  | hiredate            | sal     | comm | deptno |
+--------+-------+-----------+------+---------------------+---------+------+--------+
| 007566 | JONES | MANAGER   | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL |     20 |
| 007698 | BLAKE | MANAGER   | 7839 | 1981-05-01 00:00:00 | 2850.00 | NULL |     30 |
| 007782 | CLARK | MANAGER   | 7839 | 1981-06-09 00:00:00 | 2450.00 | NULL |     10 |
| 007788 | SCOTT | ANALYST   | 7566 | 1987-04-19 00:00:00 | 3000.00 | NULL |     20 |
| 007839 | KING  | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 | NULL |     10 |
| 007902 | FORD  | ANALYST   | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL |     20 |
+--------+-------+-----------+------+---------------------+---------+------+--------+

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 |
+--------+---------------------+----------+

显示平均工资低于2000的部门号和它的平均工资

mysql> select * from (select deptno,avg(sal) myavg from emp group by deptno) tb1 where myavg < 2000;
+--------+-------------+
| deptno | myavg       |
+--------+-------------+
|     30 | 1566.666667 |
+--------+-------------+

显示每种岗位的雇员总数，平均工资

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

3. 多表查询

顾名思义，就是在多个表中查询，多表又分为两种情况：

多表存在着明显的外键联系
多表不存在隐藏的外键联系

mysql> select * from emp;
+--------+--------+-----------+------+---------------------+---------+---------+--------+
| empno  | ename  | job       | mgr  | hiredate            | sal     | comm    | deptno |
+--------+--------+-----------+------+---------------------+---------+---------+--------+
| 007369 | SMITH  | CLERK     | 7902 | 1980-12-17 00:00:00 |  800.00 |    NULL |     20 |
| 007499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 00:00:00 | 1600.00 |  300.00 |     30 |
| 007521 | WARD   | SALESMAN  | 7698 | 1981-02-22 00:00:00 | 1250.00 |  500.00 |     30 |
| 007566 | JONES  | MANAGER   | 7839 | 1981-04-02 00:00:00 | 2975.00 |    NULL |     20 |
| 007654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 |     30 |
| 007698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 00:00:00 | 2850.00 |    NULL |     30 |
| 007782 | CLARK  | MANAGER   | 7839 | 1981-06-09 00:00:00 | 2450.00 |    NULL |     10 |
| 007788 | SCOTT  | ANALYST   | 7566 | 1987-04-19 00:00:00 | 3000.00 |    NULL |     20 |
| 007839 | KING   | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 |    NULL |     10 |
| 007844 | TURNER | SALESMAN  | 7698 | 1981-09-08 00:00:00 | 1500.00 |    0.00 |     30 |
| 007876 | ADAMS  | CLERK     | 7788 | 1987-05-23 00:00:00 | 1100.00 |    NULL |     20 |
| 007900 | JAMES  | CLERK     | 7698 | 1981-12-03 00:00:00 |  950.00 |    NULL |     30 |
| 007902 | FORD   | ANALYST   | 7566 | 1981-12-03 00:00:00 | 3000.00 |    NULL |     20 |
| 007934 | MILLER | CLERK     | 7782 | 1982-01-23 00:00:00 | 1300.00 |    NULL |     10 |
+--------+--------+-----------+------+---------------------+---------+---------+--------+mysql> select * from dept;
+--------+------------+----------+
| deptno | dname      | loc      |
+--------+------------+----------+
|     10 | ACCOUNTING | NEW YORK |
|     20 | RESEARCH   | DALLAS   |
|     30 | SALES      | CHICAGO  |
|     40 | OPERATIONS | BOSTON   |
+--------+------------+----------+
-- 以上就是明显的外键联系 deptnomysql> select * from salgrade;
+-------+-------+-------+
| grade | losal | hisal |
+-------+-------+-------+
|     1 |   700 |  1200 |
|     2 |  1201 |  1400 |
|     3 |  1401 |  2000 |
|     4 |  2001 |  3000 |
|     5 |  3001 |  9999 |
+-------+-------+-------+
-- 这个表和emp的sal联系，sal在losal~hisal之间决定grade，这种联系比较隐藏

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

通过外键联系我们就可以去重。

mysql> select ename,sal,dname from emp,dept where emp.deptno=dept.deptno;
+--------+---------+------------+
| ename  | sal     | dname      |
+--------+---------+------------+
| SMITH  |  800.00 | RESEARCH   |
| ALLEN  | 1600.00 | SALES      |
| WARD   | 1250.00 | SALES      |
| JONES  | 2975.00 | RESEARCH   |
| MARTIN | 1250.00 | SALES      |
| BLAKE  | 2850.00 | SALES      |
| CLARK  | 2450.00 | ACCOUNTING |
| SCOTT  | 3000.00 | RESEARCH   |
| KING   | 5000.00 | ACCOUNTING |
| TURNER | 1500.00 | SALES      |
| ADAMS  | 1100.00 | RESEARCH   |
| JAMES  |  950.00 | SALES      |
| FORD   | 3000.00 | RESEARCH   |
| MILLER | 1300.00 | ACCOUNTING |
+--------+---------+------------+

显示部门号为10的部门名，员工名和工资

mysql> select emp.deptno,dname,ename,sal from emp,dept where emp.deptno=dept.deptno and emp.deptno=10;
+--------+------------+--------+---------+
| deptno | dname      | ename  | sal     |
+--------+------------+--------+---------+
|     10 | ACCOUNTING | CLARK  | 2450.00 |
|     10 | ACCOUNTING | KING   | 5000.00 |
|     10 | ACCOUNTING | MILLER | 1300.00 |
+--------+------------+--------+---------+

显示各个员工的姓名，工资，及工资级别

mysql> select emp.ename,emp.sal,salgrade.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 |
+--------+---------+-------+

4. 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）
子查询

mysql> select empno,ename from emp where empno=(select mgr from emp where ename='FORD');
+--------+-------+
| empno  | ename |
+--------+-------+
| 007566 | JONES |
+--------+-------+

多表查询

mysql> select leader.empno,leader.ename from emp leader,emp worker where leader.empno = worker.mgr and worker.ename='FORD';
+--------+-------+
| empno  | ename |
+--------+-------+
| 007566 | JONES |
+--------+-------+

5. 子查询

又称作为嵌套查询，就是在select语句中再次嵌套select

5.1 单行子查询

指嵌套语句中返回单个子查询结果，如下面问题的deptno

显示SMITH同一部门的员工

mysql> select deptno,ename from emp where deptno=(select deptno from emp where ename='SMITH');
+--------+-------+
| deptno | ename |
+--------+-------+
|     20 | SMITH |
|     20 | JONES |
|     20 | SCOTT |
|     20 | ADAMS |
|     20 | FORD  |
+--------+-------+

5.2 多行子查询

指嵌套语句中返回多个子查询结果

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 job from emp where deptno=10) and deptno<>10;
+-------+---------+---------+--------+
| ename | job     | sal     | deptno |
+-------+---------+---------+--------+
| JONES | MANAGER | 2975.00 |     20 |
| BLAKE | MANAGER | 2850.00 |     30 |
| SMITH | CLERK   |  800.00 |     20 |
| ADAMS | CLERK   | 1100.00 |     20 |
| JAMES | CLERK   |  950.00 |     30 |
+-------+---------+---------+--------+

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 |
+-------+---------+--------+

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（不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) and deptno<>30;
+--------+---------+--------+
| ename  | sal     | deptno |
+--------+---------+--------+
| JONES  | 2975.00 |     20 |
| CLARK  | 2450.00 |     10 |
| SCOTT  | 3000.00 |     20 |
| KING   | 5000.00 |     10 |
| ADAMS  | 1100.00 |     20 |
| FORD   | 3000.00 |     20 |
| MILLER | 1300.00 |     10 |
+--------+---------+--------+

5.3 多列子查询

查询的条件有多个，返回多列条件

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 * from emp where (deptno,job)=(select deptno,job from emp where ename='SMITH') and ename<>'SMITH';
+--------+-------+-------+------+---------------------+---------+------+--------+
| empno  | ename | job   | mgr  | hiredate            | sal     | comm | deptno |
+--------+-------+-------+------+---------------------+---------+------+--------+
| 007876 | ADAMS | CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 | NULL |     20 |
+--------+-------+-------+------+---------------------+---------+------+--------+

5.4 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

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

mysql> select ename,emp.deptno,sal,tmp.avgsal from emp,(select deptno,avg(sal) avgsal from emp group by deptno) tmp where emp.sal > tmp.avgsal;
+-------+--------+---------+-------------+
| ename | deptno | sal     | avgsal      |
+-------+--------+---------+-------------+
| JONES |     20 | 2975.00 | 2916.666667 |
| SCOTT |     20 | 3000.00 | 2916.666667 |
| KING  |     10 | 5000.00 | 2916.666667 |
| FORD  |     20 | 3000.00 | 2916.666667 |
| JONES |     20 | 2975.00 | 2175.000000 |
| BLAKE |     30 | 2850.00 | 2175.000000 |
| CLARK |     10 | 2450.00 | 2175.000000 |
| SCOTT |     20 | 3000.00 | 2175.000000 |
| KING  |     10 | 5000.00 | 2175.000000 |
| FORD  |     20 | 3000.00 | 2175.000000 |
| ALLEN |     30 | 1600.00 | 1566.666667 |
| JONES |     20 | 2975.00 | 1566.666667 |
| BLAKE |     30 | 2850.00 | 1566.666667 |
| CLARK |     10 | 2450.00 | 1566.666667 |
| SCOTT |     20 | 3000.00 | 1566.666667 |
| KING  |     10 | 5000.00 | 1566.666667 |
| FORD  |     20 | 3000.00 | 1566.666667 |
+-------+--------+---------+-------------+

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.deptno,sal,maxsal from emp,(select deptno,max(sal) maxsal from emp group by deptno) tmp where emp.sal=tmp.maxsal;
+-------+--------+---------+---------+
| ename | deptno | sal     | maxsal  |
+-------+--------+---------+---------+
| BLAKE |     30 | 2850.00 | 2850.00 |
| SCOTT |     20 | 3000.00 | 3000.00 |
| KING  |     10 | 5000.00 | 5000.00 |
| FORD  |     20 | 3000.00 | 3000.00 |
+-------+--------+---------+---------+

显示每个部门的信息（部门名，编号，地址）和人员数量

mysql> select dept.dname,dept.deptno,dept.loc,count(*) from emp,dept where emp.deptno=dept.deptno group by dept.dname,dept.deptno,dept.loc;
+------------+--------+----------+----------+
| dname      | deptno | loc      | count(*) |
+------------+--------+----------+----------+
| ACCOUNTING |     10 | NEW YORK |        3 |
| RESEARCH   |     20 | DALLAS   |        5 |
| SALES      |     30 | CHICAGO  |        6 |
+------------+--------+----------+----------+mysql> select dept.dname,dept.deptno,dept.loc,tb1.人员数量 from dept,(select deptno,count(*) 人员数量 from emp group by deptno) tb1 where dept.deptno=tb1.deptno;
+------------+--------+----------+--------------+
| dname      | deptno | loc      | 人员数量     |
+------------+--------+----------+--------------+
| ACCOUNTING |     10 | NEW YORK |            3 |
| RESEARCH   |     20 | DALLAS   |            5 |
| SALES      |     30 | CHICAGO  |            6 |
+------------+--------+----------+--------------+