MySQL（复合查询）
2024-05-25 21:48:52
文章目录
- 0 前言
- 1 基本查询
- 2 多表查询
- 3 自连接
- 4 子查询
- 4.1 单行子查询
- 4.2 多行子查询
- 4.3 多列子查询
- 4.4 在from子句中使用子查询
- 4.5 合并查询
- 4.5.1 union
- 4.5.3 union all
0 前言
相关内容已经准备好了
- 链接：https://gitee.com/ding-xushengyun/linux__cpp/blob/master/scott_data.sql
准备工作，创建一个雇员信息表（来自oracle 9i的经典测试表）- emp员工表
- dept部门表
- salgrade工资等级表
1 基本查询
- 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 |
+--------+-------+---------+------+---------------------+---------+------+--------+
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 * 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 |
+--------+--------+-----------+------+---------------------+---------+---------+--------+
14 rows in set (0.00 sec)- 使用年薪进行降序排序
mysql> select `ename`, `sal`*12+ifnull(`comm`, 0) '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 (0.00 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
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
mysql> select `deptno`, avg(`sal`) '平均工资' from `emp` group by `deptno` having 平均工资<2000;
+--------+--------------+
| deptno | 平均工资 |
+--------+--------------+
| 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(*), format(avg(`sal`), 2) from `emp` group by `job`;
+-----------+----------+-----------------------+
| job | count(*) | format(avg(`sal`), 2) |
+-----------+----------+-----------------------+
| 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 |
+-----------+----------+-----------------------+
5 rows in set (0.00 sec)2 多表查询
多表查询本质就是穷举。
(—此图来自于相关资料)实际有效数据为下面所示：
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)- 示部门号为10的部门名，员工名和工资
mysql> select `dname`, `ename`, `sal` from `emp`, `dept` where emp.deptno=dept.deptno and emp.deptno=10;
+------------+--------+---------+
| dname | ename | sal |
+------------+--------+---------+
| ACCOUNTING | CLARK | 2450.00 |
| ACCOUNTING | KING | 5000.00 |
| ACCOUNTING | MILLER | 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 `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）
- 使用的子查询：
mysql> select empno, ename from emp where empno = (select mgr from emp where ename='FORD');
+--------+-------+
| empno | ename |
+--------+-------+
| 007566 | JONES |
+--------+-------+
1 row in set (0.02 sec)- 使用多表查询（自查询）
mysql> select e1.empno, e1.ename from emp e1, emp e2 where e1.empno=e2.mgr and e2.ename='FORD';
+--------+-------+
| empno | ename |
+--------+-------+
| 007566 | JONES |
+--------+-------+
1 row in set (0.00 sec)
4 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
4.1 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 ename from emp where deptno=(select deptno from emp where ename='SMITH');
+-------+
| ename |
+-------+
| SMITH |
| JONES |
| SCOTT |
| ADAMS |
| FORD |
+-------+
5 rows in set (0.00 sec)4.2 多行子查询
返回多行记录的子查询
- 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 deptnoo=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；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；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
- 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。
- 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, format(myavg, 2) from emp, (select avg(sal) myavg, deptno from emp groupp by deptno) tmp where emp.deptno=tmp.deptno and emp.sal>tmp.myavg;
+-------+--------+---------+------------------+
| ename | deptno | sal | format(myavg, 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 ename, sal, deptno, maxsal from emp, (select max(sal) maxsal from emp group by deptno) tmp where sal=maxsal;
+-------+---------+--------+---------+
| ename | sal | deptno | maxsal |
+-------+---------+--------+---------+
| 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, dept.dname, dept.loc, count from dept, (select deptno, count(*) count from emp groupp by deptno) tmp where tmp.deptno=dept.deptno;
+--------+------------+----------+-------+
| deptno | dname | loc | count |
+--------+------------+----------+-------+
| 10 | ACCOUNTING | NEW YORK | 3 |
| 20 | RESEARCH | DALLAS | 5 |
| 30 | SALES | CHICAGO | 6 |
+--------+------------+----------+-------+
3 rows in set (0.01 sec)4.5 合并查询
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。
- 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)4.5.3 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='MAANAGER';
+-------+---------+-----------+
| 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 (0.01 sec)MySQL（复合查询）相关推荐
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