比较表并排除值

Question

I have two schemas named as "t3" and "r1". Both have the columns "Permission". Through sql query; I want to Get the list of all permissions from "t3" and excludes the permission from "r1". I am not really into sql that's why it is confusing me a lot.

Answer 1

select *
from t3 
where t3.Permission not in (select Permission from r1)

In general, it looks like you need something like that. Although the question is not entirely clear. This is not the most productive option, if there is a lot of data, you can rewrite it in join and it will be more correct.

Answer 2

I would recommend not exists : it seems like a straight-forward approach to your querstion; also it usually scales better than [not] in when the number of row increases - and it is null-safe (as opposed to not in ):

select t3.permissions
from t3
where not exists (select 1 from r1 where r1.permissions = t3.permissions)