mysql的表连接（left|right）join
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时间：2015年06月12日
测试MYSQL表关于内外连接 表一：雇员表（雇员ID,雇员名称，雇员入职时间，薪水，部门号） create table empo( empoid int(6) not null primary key auto_increment, empname varchar(32) not null, empdate datetime not null, salary int(6) not null , deptno int(6) not null )engine=innodb charset=utf8 insert into empo values(1,‘zhangsan‘,‘2012-2-20 10:00:00‘,6000,1); insert into empo values(2,‘lisi‘,‘2013-2-20 10:00:00‘,6000,2); insert into empo values(3,‘王五‘,‘2014-2-20 10:00:00‘,6000,1); insert into empo values(4,‘zhaoliu‘,‘2015-2-20 10:00:00‘,6000,3); insert into empo values(5,‘zhaoliu‘,‘2015-2-20 10:00:00‘,6000,6); insert into empo values(6,‘zhaoliu‘,‘2015-2-20 10:00:00‘,6000,8); 表二（部门号，部门名称） create table dept( deptid int(6) primary key , deptname varchar(32) not null )engine=innodb charset=utf8 insert into dept values(1,‘xinzhengbu‘); insert into dept values(2,‘jixubu‘); insert into dept values(3,‘yunying‘); insert into dept values(3,‘shejibu‘); 题目： 例1：内连接（内连接实际上就是利用 where 子句对两张表形成的笛卡尔积进行筛选,） mysql> select * from empo,dept; +--------+----------+---------------------+--------+--------+--------+------------+ | empoid | empname | empdate | salary | deptno | deptid | deptname | +--------+----------+---------------------+--------+--------+--------+------------+ | 1 | zhangsan | 2012-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu | | 2 | lisi | 2013-02-20 10:00:00 | 6000 | 2 | 1 | xinzhengbu | | 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu | | 4 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 3 | 1 | xinzhengbu | | 1 | zhangsan | 2012-02-20 10:00:00 | 6000 | 1 | 2 | jixubu | | 2 | lisi | 2013-02-20 10:00:00 | 6000 | 2 | 2 | jixubu | | 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 2 | jixubu | | 4 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 3 | 2 | jixubu | | 1 | zhangsan | 2012-02-20 10:00:00 | 6000 | 1 | 3 | yunying | | 2 | lisi | 2013-02-20 10:00:00 | 6000 | 2 | 3 | yunying | | 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 3 | yunying | | 4 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 3 | 3 | yunying | | 1 | zhangsan | 2012-02-20 10:00:00 | 6000 | 1 | 4 | shejibu | | 2 | lisi | 2013-02-20 10:00:00 | 6000 | 2 | 4 | shejibu | | 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 4 | shejibu | | 4 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 3 | 4 | shejibu | +--------+----------+---------------------+--------+--------+--------+------------+ 16 rows in set (0.00 sec) mysql> select * from empo inner join dept; +--------+----------+---------------------+--------+--------+--------+------------+ | empoid | empname | empdate | salary | deptno | deptid | deptname | +--------+----------+---------------------+--------+--------+--------+------------+ | 1 | zhangsan | 2012-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu | | 2 | lisi | 2013-02-20 10:00:00 | 6000 | 2 | 1 | xinzhengbu | | 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu | | 4 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 3 | 1 | xinzhengbu | | 1 | zhangsan | 2012-02-20 10:00:00 | 6000 | 1 | 2 | jixubu | | 2 | lisi | 2013-02-20 10:00:00 | 6000 | 2 | 2 | jixubu | | 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 2 | jixubu | | 4 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 3 | 2 | jixubu | | 1 | zhangsan | 2012-02-20 10:00:00 | 6000 | 1 | 3 | yunying | | 2 | lisi | 2013-02-20 10:00:00 | 6000 | 2 | 3 | yunying | | 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 3 | yunying | | 4 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 3 | 3 | yunying | | 1 | zhangsan | 2012-02-20 10:00:00 | 6000 | 1 | 4 | shejibu | | 2 | lisi | 2013-02-20 10:00:00 | 6000 | 2 | 4 | shejibu | | 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 4 | shejibu | | 4 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 3 | 4 | shejibu | +--------+----------+---------------------+--------+--------+--------+------------+ 16 rows in set (0.00 sec) 上面两个SQL等价的。 下面是加where条件的等价SQL(select * from empo,dept where deptno=deptid;) mysql> select * from empo inner join dept on deptno=deptid; +--------+----------+---------------------+--------+--------+--------+------------+ | empoid | empname | empdate | salary | deptno | deptid | deptname | +--------+----------+---------------------+--------+--------+--------+------------+ | 1 | zhangsan | 2012-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu | | 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu | | 2 | lisi | 2013-02-20 10:00:00 | 6000 | 2 | 2 | jixubu | | 4 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 3 | 3 | yunying | +--------+----------+---------------------+--------+--------+--------+------------+ 4 rows in set (0.00 sec) 例2：左连接 mysql> select * from empo left join dept on deptno=deptid; +--------+----------+---------------------+--------+--------+--------+------------+ | empoid | empname | empdate | salary | deptno | deptid | deptname | +--------+----------+---------------------+--------+--------+--------+------------+ | 1 | zhangsan | 2012-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu | | 2 | lisi | 2013-02-20 10:00:00 | 6000 | 2 | 2 | jixubu | | 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu | | 4 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 3 | 3 | yunying | +--------+----------+---------------------+--------+--------+--------+------------+ 4 rows in set (0.00 sec) 例3：右连接 mysql> select * from empo right join dept on deptno=deptid; +--------+----------+---------------------+--------+--------+--------+------------+ | empoid | empname | empdate | salary | deptno | deptid | deptname | +--------+----------+---------------------+--------+--------+--------+------------+ | 1 | zhangsan | 2012-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu | | 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu | | 2 | lisi | 2013-02-20 10:00:00 | 6000 | 2 | 2 | jixubu | | 4 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 3 | 3 | yunying | | NULL | NULL | NULL | NULL | NULL | 4 | shejibu | +--------+----------+---------------------+--------+--------+--------+------------+ 5 rows in set (0.00 sec) 例4：将子查询替换成连接 表1 mysql> select * from empo; +--------+----------+---------------------+--------+--------+ | empoid | empname | empdate | salary | deptno | +--------+----------+---------------------+--------+--------+ | 1 | zhangsan | 2012-02-20 10:00:00 | 6000 | 1 | | 2 | lisi | 2013-02-20 10:00:00 | 6000 | 2 | | 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | | 4 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 3 | | 5 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 6 | | 6 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 8 | +--------+----------+---------------------+--------+--------+ 6 rows in set (0.00 sec) 表2 mysql> select * from dept; +--------+------------+ | deptid | deptname | +--------+------------+ | 1 | xinzhengbu | | 2 | jixubu | | 3 | yunying | | 4 | shejibu | +--------+------------+ 4 rows in set (0.00 sec) 题目1、找出雇员不在部门表中的用户（雇员ID号为5,6的不在部门列表中） select * from empo where deptno not in (select deptid from dept) 子查询写法 mysql> select * from empo where deptno not in (select deptid from dept); +--------+---------+---------------------+--------+--------+ | empoid | empname | empdate | salary | deptno | +--------+---------+---------------------+--------+--------+ | 5 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 6 | | 6 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 8 | +--------+---------+---------------------+--------+--------+ 内连接写法(和上面写法同等） mysql> select * from empo left join dept on empo.deptno=dept.deptid where deptid is NULL; +--------+---------+---------------------+--------+--------+--------+----------+ | empoid | empname | empdate | salary | deptno | deptid | deptname | +--------+---------+---------------------+--------+--------+--------+----------+ | 5 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 6 | NULL | NULL | | 6 | zhaoliu | 2015-02-20 10:00:00 | 6000 | 8 | NULL | NULL | +--------+---------+---------------------+--------+--------+--------+----------+ 说明：mysql中join中使用where和on的区别 1.(left|right)join... on.. and 的写法：是先处理on后面的条件，在处理表之间的连接 2.(left|rgint)join... on.. where的写法： 是先表left连接，在处理where条件
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