在前面的笔记中做的查询基本都是对一张表进行查询，在实际开发中远远不够，本篇文章内容是复合查询相关的笔记。需要用到oracle9i的经典测试表，在笔记（六）中已经教大家如何导入了。

复合查询

  • 基本查询回顾
  • 多表查询
  • 子连接
  • 子查询
    • 单行子查询
    • 多行子查询
    • 多列子查询
    • 在 from 子句中使用子查询
    • 合并查询

基本查询回顾

这是 emp 表

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 |+--------+--------+-----------+------+---------------------+---------+---------+--------+14 rows in set (0.00 sec)
  • 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 |+--------+-------+---------+------+---------------------+---------+------+--------+2 rows in set (0.00 sec)
  • 按照部门号升序而雇员的工资降序排序
mysql> select ename,deptno,sal from emp order by deptno asc,sal desc;+--------+--------+---------+| ename| deptno | sal |+--------+--------+---------+| KING | 10 | 5000.00 || CLARK| 10 | 2450.00 || MILLER | 10 | 1300.00 || SCOTT| 20 | 3000.00 || FORD | 20 | 3000.00 || JONES| 20 | 2975.00 || ADAMS| 20 | 1100.00 || SMITH| 20 |800.00 || BLAKE| 30 | 2850.00 || ALLEN| 30 | 1600.00 || TURNER | 30 | 1500.00 || WARD | 30 | 1250.00 || MARTIN | 30 | 1250.00 || JAMES| 30 |950.00 |+--------+--------+---------+14 rows in set (0.00 sec)
  • 使用年薪进行降序排序

这里的年薪等于表中的 sal（工资）* 12 + comm （奖金） ，comm 可能为null,不能直接相加，所以需要用到 ifnull 函数，ifnull（comm,0）表示如果comm为空，则使用 0

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)
  • 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 (0.01 sec)
  • 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)
  • 显示每个部门的平均工资和最高工资

这里是要求每个部门的平均工资和最高工资，则要用到分组查询，在每个部门内比较平均工资和最高工资。

mysql> select deptno, avg(sal),max(sal) from emp group by deptno;+--------+-------------+----------+| deptno | avg(sal)| max(sal) |+--------+-------------+----------+| 10 | 2916.666667 |5000.00 || 20 | 2175.000000 |3000.00 || 30 | 1566.666667 |2850.00 |+--------+-------------+----------+3 rows in set (0.00 sec)
  • 显示平均工资低于2000的部门号和它的平均工资

这里和前一个案例一样，也是需要用到分组查询，分组查询后需要用 having 配合筛选

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)
  • 显示每种岗位的雇员总数，平均工资
mysql> select job,count(*) as 人数 ,avg(sal) as 平均工资 from emp group by job;+-----------+--------+--------------+| job | 人数 | 平均工资 |+-----------+--------+--------------+| ANALYST |2 |3000.000000 || CLERK |4 |1037.500000 || MANAGER |3 |2758.333333 || PRESIDENT |1 |5000.000000 || SALESMAN|4 |1400.000000 |+-----------+--------+--------------+5 rows in set (0.00 sec)

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。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。

案例：

  • 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。
mysql> select* from emp,dept;


上图是联合查询的结果，具体联合方式如下图：

所以一共会有 14 * 4 = 56 条数据，但是我们从图中看到，直接联合查询而不加筛选条件，表中的一些数据是没有意义的，比如下图SMITH对应的部门号应该只有20才对。

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

mysql> select* from emp,dept where emp.deptno=dept.deptno;+--------+--------+-----------+------+---------------------+---------+---------+--------+--------+------------+----------+| empno| ename| job | mgr| hiredate| sal | comm| deptno | deptno | dname| loc|+--------+--------+-----------+------+---------------------+---------+---------+--------+--------+------------+----------+| 007369 | SMITH| CLERK | 7902 | 1980-12-17 00:00:00 |800.00 |NULL | 20 | 20 | RESEARCH | DALLAS || 007499 | ALLEN| SALESMAN| 7698 | 1981-02-20 00:00:00 | 1600.00 |300.00 | 30 | 30 | SALES| CHICAGO|| 007521 | WARD | SALESMAN| 7698 | 1981-02-22 00:00:00 | 1250.00 |500.00 | 30 | 30 | SALES| CHICAGO|| 007566 | JONES| MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 |NULL | 20 | 20 | RESEARCH | DALLAS || 007654 | MARTIN | SALESMAN| 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 | 30 | 30 | SALES| CHICAGO|| 007698 | BLAKE| MANAGER | 7839 | 1981-05-01 00:00:00 | 2850.00 |NULL | 30 | 30 | SALES| CHICAGO|| 007782 | CLARK| MANAGER | 7839 | 1981-06-09 00:00:00 | 2450.00 |NULL | 10 | 10 | ACCOUNTING | NEW YORK || 007788 | SCOTT| ANALYST | 7566 | 1987-04-19 00:00:00 | 3000.00 |NULL | 20 | 20 | RESEARCH | DALLAS || 007839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 |NULL | 10 | 10 | ACCOUNTING | NEW YORK || 007844 | TURNER | SALESMAN| 7698 | 1981-09-08 00:00:00 | 1500.00 |0.00 | 30 | 30 | SALES| CHICAGO|| 007876 | ADAMS| CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 |NULL | 20 | 20 | RESEARCH | DALLAS || 007900 | JAMES| CLERK | 7698 | 1981-12-03 00:00:00 |950.00 |NULL | 30 | 30 | SALES| CHICAGO|| 007902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 |NULL | 20 | 20 | RESEARCH | DALLAS || 007934 | MILLER | CLERK | 7782 | 1982-01-23 00:00:00 | 1300.00 |NULL | 10 | 10 | ACCOUNTING | NEW YORK |+--------+--------+-----------+------+---------------------+---------+---------+--------+--------+------------+----------+14 rows in set (0.00 sec)
  • 显示部门号为10的部门名，员工名和工资
mysql> select ename,dname,sal from emp,dept where emp.deptno = dept.deptno and dept.deptno = 10;+--------+------------+---------+| ename| dname| sal |+--------+------------+---------+| CLARK| ACCOUNTING | 2450.00 || KING | ACCOUNTING | 5000.00 || MILLER | ACCOUNTING | 1300.00 |+--------+------------+---------+3 rows in set (0.00 sec)
  • 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)

子连接

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）

  • 使用子查询的方法：
mysql> select empno,ename from emp where emp.empno = (select mgr from emp where ename = 'FORD');+--------+-------+| empno| ename |+--------+-------+| 007566 | JONES |+--------+-------+1 row in set (0.00 sec)
  • 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 as leader,emp as worker where leader.empno=worker.mgr and worker.ename='FORD';+--------+-------+| empno| ename |+--------+-------+| 007566 | JONES |+--------+-------+1 row in set (0.00 sec)

子查询

子查询是指嵌入在其他sql语句中的select语句，也叫嵌套查询

单行子查询

返回一行记录的子查询

  • 显示SMITH同一部门的员工
mysql> select* from emp where deptno=(select deptno from emp where ename='SMITH');+--------+-------+---------+------+---------------------+---------+------+--------+| empno| ename | job | mgr| hiredate| sal | comm | deptno |+--------+-------+---------+------+---------------------+---------+------+--------+| 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 |800.00 | NULL | 20 || 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 || 007788 | SCOTT | ANALYST | 7566 | 1987-04-19 00:00:00 | 3000.00 | NULL | 20 || 007876 | ADAMS | CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 | NULL | 20 || 007902 | FORD| ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL | 20 |+--------+-------+---------+------+---------------------+---------+------+--------+5 rows in set (0.00 sec)

多行子查询

返回多行记录的子查询

  • in 关键字：MySQL中的IN关键字用于判断某个字段的值是否在指定的集合中。如果字段的值在集合中，则满足条件，该字段所在的数据将会被查询出来。

案例：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 |+-------+---------+---------+--------+| 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 |+-------+---------+---------+--------+5 rows in set (0.00 sec)
  • all 关键字：会列举出所有查询到的结果，通常与where使用，作比较。

案例：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)
  • any 关键字：通常和where一起使用，any关键词可以理解为“对于子查询返回的列中的任一数值，如果比较结果为true，则返回true”。

案例：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)

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)

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。

案例：

  • 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) as asal,deptno as dt from emp group by deptno) as 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)
  • 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) as 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)
  • 显示每个部门的信息（部门名，编号，地址）和人员数量
mysql> select dept.deptno,dname,mycnt,loc from dept,(select count(*) as mycnt,deptno from emp group by deptno) as 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)

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

  • 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';+-------+---------+-----------+| 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)
  • 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。
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)