图解SQL的inner join、left join、right join、full outer join、union、union all的区别

https://www.cnblogs.com/logon/p/3748020.html

select 1, 2, 3, area_id, 4, 5, 6 from t_main_work mv inner join t_work w on mv_target=w.id inner join t_area a on a.id=w.area_id