从表中选择数据并从另一个表中填充特定值

Question

I have two tables discussions and votes that are like this

discussions

votes

that parentId in votes is id in discussions table

but exist a problem

I want to have a key with name likeByMe and want to fill this key when select discussions for specific user. how can I connect these two tables and fill this value when call one query?

I want something like this

select * 
from discussions

and fill likeByMe from votes table for any rows by true or false value

Answer 1

Given your description, you can use exists :

select d.*,
       (exists (select 1
                from votes v
                where v.parentid = d.id and v.userid = ?
               )
       ) as likedByMe
from discussions d;

The ? is a parameter placeholder for the user you care about.