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7-MySQL_复合查询

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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)

7.1 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 | +--------+-------+---------+------+---------------------+---------+------+--------+

按照部门号升序而雇员的工资降序排序

mysql> select * from emp order by empno asc , sal desc; +--------+--------+-----------+------+---------------------+---------+---------+--------+ | 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 | +--------+--------+-----------+------+---------------------+---------+---------+--------+

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)

显示工资高于平均工资的员工信息

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)

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) 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(*) ,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)

7.2 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。

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

7.3 自连接

自连接是指在同一张表连接查询

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

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 leader, emp worker whereleader.empno = worker.mgr and worker.ename='FORD'; +--------+-------+ | empno | ename | +--------+-------+ | 007566 | JONES | +--------+-------+ 1 row in set (0.00 sec)

7.4 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

7.4.1 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 * from emp where deptno = (select deptno from emp where enamee='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)

7.4.2 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 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；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 fromemp 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)

7.4.3 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 fromemp where ename='SMITH') and ename <> 'SMITH'; +-------+ | ename | +-------+ | ADAMS | +-------+ 1 row in set (0.00 sec)

7.4.4 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。

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

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 annd 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 (0.01 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) 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

方法1：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2：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)

7.4.5 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

7.4.5.1 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'; +-------+---------+-----------+ | 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)

7.4.5.2 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)

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