数値がゼロになるだけでカウントがNULLを返す

Question

ユーザーの信頼性を追跡するテーブルがあります。

+-----------------+-----------------+-------------+ 
| user_id_1  | user_id_2  | is_trusted | 
+-----------------+-----------------+-------------+ 
| 1    | 2    | 0   | 
... 

ここで、1は信頼され、0は信頼できません。否定的なフィードバックがない場合は、値としてNULLが返されます。正に - 0を得る方法はありますか？

select tr2.user_id_2 user, 
    ((select count(*) plus 
     from trust_ratings tr 
     where is_trusted = 1 and 
     tr2.user_id_2 = tr.user_id_2 
     group by tr.user_id_2) 
    - 
    (select count(*) minus 
     from trust_ratings tr 
     where is_trusted = 0 and 
     tr2.user_id_2 = tr.user_id_2 
     group by tr.user_id_2)) as score 
    from trust_ratings tr2 
    group by user; 

Answer 1

あなたはcase when使用することができますあなたが個別に各クエリを試してみました

select user_id_2 user, 
     sum(is_trusted * 2 - 1) as score 
    from trust_ratings 
group by user; 

Answer 2

使用COALESCE()：

select tr2.user_id_2 user, 
    (
     coalesce(
     (select count(*) plus 
     from trust_ratings tr 
     where is_trusted = 1 and 
     tr2.user_id_2 = tr.user_id_2 
     group by tr.user_id_2), 0) 
    - 
     coalesce(
     (select count(*) minus 
     from trust_ratings tr 
     where is_trusted = 0 and 
     tr2.user_id_2 = tr.user_id_2 
     group by tr.user_id_2), 0) 
    ) as score 
    from trust_ratings tr2 
    group by user;