Mysql中常用的几种join连接方式总结

1.首先准备两张表

部门表：

员工表：

以下我们就对这两张表进行不同的连接操作

1.内连接

作用： 查询两张表的共有部分

语句：Select from tableA A Inner join tableB B on A.Key = B.Key

示例：SELECT * from employee e INNER JOIN department d on e.dep_id = d.id;

结果显示：通过这个查找的方法，我们没有查到id为8的数据

2.左连接

作用：把左边表的内容全部查出,右边表只查出满足条件的记录

语句：Select from tableA A Left Join tableB B on A.Key = B.Key

示例：SELECT * from employee e LEFT JOIN department d on e.dep_id = d.id;

结果显示：

3.右连接

作用：把右边表的内容全部查出,左边表只查出满足条件的记录

语句：Select from tableA A Left Join tableB B on A.Key = B.Key

示例：SELECT * from employee e RIGHT JOIN department d on e.dep_id = d.id;

结果显示：

4.查询左表独有数据

作用：查询A的独有数据

语句：Select from tableA A Left Join tableB B on A.Key = B.Key where B.key IS NULL

示例：SELECT * from employee e LEFT JOIN department d on e.dep_id = d.id WHERE d.id IS NULL;

结果显示：

5.查询右表独有数据

作用：查询B的独有数据

语句：Select from tableA A Right Join tableB B on A.Key = B.Key where A.key IS NULL

示例：SELECT * from employee e RIGHT JOIN department d on e.dep_id = d.id WHERE e.id IS NULL;

结果显示：

6.全连接

作用：查询两个表的全部信息

语句：Select from tableA A Full Outter Join tableB B on A.Key = B.Key

注:Mysql 默认不支持此种写法 Oracle支持       可以使用将左连接与右连接结合起来作为全连接

示例：

SELECT * from employee e LEFT JOIN department d on e.dep_id = d.id
UNION
SELECT * from employee e RIGHT JOIN department d on e.dep_id = d.id

结果显示：

7.查询左右表各自的独有的数据

作用：查询A和B各自的独有的数据

语句：Select from tableA A Full Outter Join tableB B on A.Key = B.Key where A.key = null or B.key=null

示例：

SELECT * from employee e LEFT JOIN department d on e.dep_id = d.id WHERE d.id is NULL
UNION
SELECT * from employee e RIGHT JOIN department d on e.dep_id = d.id WHERE e.dep_id is NULL

结果显示：

总结