MYSQL——复合查询

一、多表查询

1.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)

2.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 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)

二、自连接

在同一张表上面查询
1.显示员工FORD的上级领导的编号和姓名
（1）子查询：

mysql> select MGR from EMP where ENAME='FORD';
+------+
| MGR  |
+------+
| 7566 |
+------+
1 row in set (0.00 sec)

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

（2）多表查询（自查询）：需要用到重名

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

三、子查询

子查询可以出现的两个地方：

1. where子句中，作为筛选条件使用
2. from子句中，用来和特定的表做笛卡尔积

子查询是指嵌入在其他sql语句中的select语句，也叫嵌套查询

1.单行子查询:返回一行记录的子查询

(1)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 |
+-------+-------+---------+------+------------+---------+------+--------+
|  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 | 1987-04-19 | 3000.00 | NULL |     20 |
|  7876 | ADAMS | CLERK   | 7788 | 1987-05-23 | 1100.00 | NULL |     20 |
|  7902 | FORD  | ANALYST | 7566 | 1981-12-03 | 3000.00 | NULL |     20 |
+-------+-------+---------+------+------------+---------+------+--------+
5 rows in set (0.00 sec)

2.多行子查询

（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 deptno,sal from EMP where deptno=30;
+--------+---------+
| deptno | sal     |
+--------+---------+
|     30 | 1600.00 |
|     30 | 1250.00 |
|     30 | 1250.00 |
|     30 | 2850.00 |
|     30 | 1500.00 |
|     30 |  950.00 |
+--------+---------+
6 rows in set (0.00 sec)

mysql> select distinct sal from EMP where deptno=30;
+---------+
| sal     |
+---------+
| 1600.00 |
| 1250.00 |
| 2850.00 |
| 1500.00 |
|  950.00 |
+---------+
5 rows in set (0.00 sec)

mysql> select ename,sal,deptno from EMP where sal > all(select distinct 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 distinct sal from EMP where deptno=30;
+---------+
| sal     |
+---------+
| 1600.00 |
| 1250.00 |
| 2850.00 |
| 1500.00 |
|  950.00 |
+---------+
5 rows in set (0.00 sec)

mysql> select ename,sal,deptno from EMP where sal > any(select distinct 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)

all与any的区别：all是所有都比较，any是比较其中一个

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
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');
+-------+-------+-------+------+------------+---------+------+--------+
| EMPNO | ENAME | JOB   | MGR  | HIREDATE   | SAL     | COMM | DEPTNO |
+-------+-------+-------+------+------------+---------+------+--------+
|  7369 | SMITH | CLERK | 7902 | 1980-12-17 |  800.00 | NULL |     20 |
|  7876 | ADAMS | CLERK | 7788 | 1987-05-23 | 1100.00 | NULL |     20 |
+-------+-------+-------+------+------------+---------+------+--------+
2 rows in set (0.00 sec)

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 |
+-------+-------+-------+------+------------+--------+------+--------+
|  7369 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | NULL |     20 |
+-------+-------+-------+------+------------+--------+------+--------+
1 row in set (0.00 sec)

4.from中使用的子查询：把一个子查询当成一个临时表使用

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,deptno,sal,avg(sal) from EMP,(select avg(sal) asal,deptno dep from EMP group by depptno) tmp where EMP.sal > tmp.asal and EMP.deptno=tmp.dep;
+-------+--------+---------+-------------+
| ename | deptno | sal     | avg(sal)    |
+-------+--------+---------+-------------+
| KING  |     10 | 5000.00 | 3070.833333 |
+-------+--------+---------+-------------+
1 row 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 ename,deptno,sal,_max from EMP,(select deptno dt,max(sal) _max from EMP group by dt) max__tb where EMP.deptno=max_tb.dt and EMP.sal=max_tb._max;
+-------+--------+---------+---------+
| ename | deptno | sal     | _max    |
+-------+--------+---------+---------+
| BLAKE |     30 | 2850.00 | 2850.00 |
| SCOTT |     20 | 3000.00 | 3000.00 |
| KING  |     10 | 5000.00 | 5000.00 |
| FORD  |     20 | 3000.00 | 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 *from DEPT,(select deptno dt,count(*) 总数 from EMP group by dt) total where DEPT.deptno==total.dt;
+--------+------------+----------+------+--------+
| DEPTNO | DNAME      | LOC      | dt   | 总数   |
+--------+------------+----------+------+--------+
|     10 | ACCOUNTING | NEW YORK |   10 |      3 |
|     20 | RESEARCH   | DALLAS   |   20 |      5 |
|     30 | SALES      | CHICAGO  |   30 |      6 |
+--------+------------+----------+------+--------+
3 rows in set (0.00 sec)

mysql> select dname,deptno,loc,总数 from DEPT,(select deptno dt,count(*) 总数 from EMP group by dt) tottal where DEPT.deptno=total.dt;
+------------+--------+----------+--------+
| dname      | deptno | loc      | 总数   |
+------------+--------+----------+--------+
| ACCOUNTING |     10 | NEW YORK |      3 |
| RESEARCH   |     20 | DALLAS   |      5 |
| SALES      |     30 | CHICAGO  |      6 |
+------------+--------+----------+--------+
3 rows in set (0.00 sec)

5.合并查询

（1）union：作用于取两个结果集的并集，且会自动去掉重复行(左侧查询的列与右侧查询的列数要一样)

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;
+-------+---------+-----------+
| ename | sal     | job       |
+-------+---------+-----------+
| JONES | 2975.00 | MANAGER   |
| BLAKE | 2850.00 | MANAGER   |
| SCOTT | 3000.00 | ANALYST   |
| KING  | 5000.00 | PRESIDENT |
| FORD  | 3000.00 | ANALYST   |
+-------+---------+-----------+
5 rows in set (0.00 sec)

mysql> select ename,sal,job from EMP where job='MANAGER';
+-------+---------+---------+
| ename | sal     | job     |
+-------+---------+---------+
| JONES | 2975.00 | MANAGER |
| BLAKE | 2850.00 | MANAGER |
| CLARK | 2450.00 | MANAGER |
+-------+---------+---------+
3 rows in set (0.00 sec)

mysql> select ename,sal,job from EMP where sal > 2500
    -> union
    -> select ename,sal,job,from EMP where job='MANAGER';
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'from EMP where job='MANAGER'' at line 3
mysql> select ename,sal,job from EMP where sal > 2500 union select ename,sal,job from EMP where job='MAANAGER';
+-------+---------+-----------+
| 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)

（2）union all：不做去重

mysql> select ename,sal,job from EMP where sal > 2500 union all select ename,sal,job from EMP where jobb='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)