mysql 的几种连接方式

表一 user(用户表)

表二 dept(部门表)

外连接

select * from user u left join dept d on u.dept = d.id where d.id is null;

左外连接

select * from user u left join dept d on u.dept = d.id;

全连接

    -- 左独有数据
select * from user u left join dept d on u.dept = d.id where d.id is null
union
    -- 右独有数据
select * from user u right join dept d on u.dept = d.id where  u.id is null;

全外连接

    -- 左外
select * from user u left join dept d on u.dept = d.id
union
    -- 右外
select * from user u right join dept d on u.dept = d.id;