SQL 查询未在 SUM 和 COUNT 中找到所有行

Question

select coalesce(ratings.positive,0) as positive,coalesce(ratings.negative,0) as negative,articles.id,x.username,commentnumb, 
    articles.category,
    articles."createdAt",
    articles.id,
    articles.title,
    articles."updatedAt"
    FROM articles
    LEFT JOIN (SELECT id AS userId,username,about FROM users) x ON articles.user_id = x.userId
    LEFT JOIN (SELECT id,
        article_id,
        sum(case when rating = '1' then 1 else 0 end) as positive,
        sum(case when rating = '0' then 1 else 0 end) as negative
        from article_ratings
        GROUP by id
        ) as ratings ON ratings.article_id = articles.id
    LEFT JOIN (SELECT article_id,id,
       count(article_id) as commentNumb
       from article_comments
       GROUP by id
       ) as comments ON comments.article_id = articles.id
    WHERE articles."createdAt" <= :date
    group by ratings.positive,ratings.negative,articles.id,x.username,commentnumb
    order by articles."createdAt" desc
    LIMIT 10

The code is working, however I have many more comments and many more ratings than what is counted in both SUM and COUNT functions.

How do I fix this query?

This is using postgres.

I've done some experimentation and it seems that the third join for comments is the one causing issues.

Answer 1

In the derived tables, you should ideally be grouping using article_id. But, you are grouping based on id. Due to this, you are getting more than the necessary rows in the derived tables. I have modified the query to suit your needs.

    SELECT COALESCE(ratings.positive,0) AS positive,COALESCE(ratings.negative,0) AS negative,articles.id,x.username,commentnumb, 
        articles.category,
        articles."createdAt",
        articles.id,
        articles.title,
        articles."updatedAt"
        FROM articles
        LEFT OUTER JOIN (SELECT id AS userId,username,about FROM users) x ON articles.user_id = x.userId
        LEFT OUTER JOIN (SELECT article_id,
            SUM(case when rating = '1' then 1 else 0 end) as positive,
            SUM(case when rating = '0' then 1 else 0 end) as negative
            FROM article_ratings
            GROUP by article_id 
            ) AS ratings ON ratings.article_id = articles.id
        LEFT OUTER JOIN (SELECT article_id,
           count(article_id) as commentNumb
           FROM article_comments
           GROUP by article_id
           ) AS comments ON comments.article_id = articles.id
        WHERE articles."createdAt" <= :date
        ORDER BY articles."createdAt" desc
        LIMIT 10;