连表操作

内连接：只取两张表的共同部分

　　select * from employee inner join department on employee.dep_id = department.id;

　　

左连接：在内连接的基础上保留左表的记录

　　select * from employee left join department on employee.dep_id = department.id;

 

右连接：在内连接的基础上保留右表的记录

　　select * from employee right join department on employee.dep_id = department.id;

全外连接：在内连接的基础上保留左右两边没有对应关系的记录

　　select * from employee left join department on employee.dep_id = department.id

　　union

　　select * from employee right join department on employee.dep_id = department.id;