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：
