zzz1
| uid | is_delete |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 0 |
| zzz2 |
| uid | is_delete |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 0 |
select * from zzz1 left join zzz2 on zzz1.uid = zzz2.uid
where zzz1.is_delete = 0 and zzz2.is_delete = 0
结果: 3 0 3 0
select * from (select * from zzz1 where zzz1.is_delete = 0) z1
left join (select * from zzz2 where zzz2.is_delete = 0) z2
on z1.uid = z2.uid
结果: 2 0 NULL NULL 3 0 3 0
select * from (select * from zzz1 where zzz1.is_delete = 0) z1
left join (select * from zzz2 where zzz2.is_delete = 0) z2
on z1.uid = z2.uid where z2.uid is not null
结果: 3 0 3 0
select * from (select * from zzz1 where zzz1.is_delete = 0) z1
inner join (select * from zzz2 where zzz2.is_delete = 0) z2
on z1.uid = z2.uid
结果: 3 0 3 0
on的过滤条件只对右表有效