按 PostgreSQL 中多个内部连接的条件计数

Question

我有以下 tables:

User
UserPostView
Post

UserPostView 是一个连接 table，其中包含有关 User 在查看 post.

后是否赞成、反对或通过的附加信息

Post 有一列 postable_type 指示 post 的类型（TextPost、ImagePost 等）。

我想计算按 postable_type 分组的每个用户的赞成票、反对票和通过计数。

我当前的查询非常慢，我很确定它可以轻松优化。

SELECT
    U.id,
    count((UP.postable_type = 'text_post' AND UPV.passed = true) OR NULL) as text_posts_pass_count,
    count((UP.postable_type = 'text_post' AND UPV.upvote = true) OR NULL) as text_posts_upvote_count,
    count((UP.postable_type = 'text_post' AND UPV.downvote = true) OR NULL) as text_posts_downvote_count,
    count((UP.postable_type = 'image_post' AND UPV.passed = true) OR NULL) as image_posts_pass_count,
    count((UP.postable_type = 'image_post' AND UPV.upvote = true) OR NULL) as image_posts_upvote_count,
    count((UP.postable_type = 'image_post' AND UPV.downvote = true) OR NULL) as image_posts_downvote_count
FROM
    users U
    INNER JOIN(
        SELECT
            user_id,
            post_id,
            passed,
            upvoted,
            downvoted
        FROM 
            user_post_views
    ) UPV on U.id :: TEXT = UPV.user_id :: TEXT
    INNER JOIN(
        SELECT
            id,
            postable_type
        FROM
            posts
    ) UP on UPV.post_id :: TEXT = UP.id :: TEXT
GROUP BY
    U.id

Answer 1

不要对联接进行类型转换！我想你只需要：

SELECT UPV.user_id,
       COUNT(*) FILTER (WHERE p.postable_type = 'text_post' AND upv.passed) as text_posts_pass_count,
       COUNT(*) FILTER (WHERE p.postable_type = 'text_post' AND upv.upvote) as text_posts_upvote_count,
       COUNT(*) FILTER (WHERE p.postable_type = 'text_post' AND upv.downvote ) as text_posts_downvote_count,
       COUNT(*) FILTER (WHERE p.postable_type = 'image_post' AND upv.passed) as image_posts_pass_count,
       COUNT(*) FILTER (WHERE p.postable_type = 'image_post' AND upv.upvote) as image_posts_upvote_count,
       COUNT(*) FILTER (WHERE p.postable_type = 'image_post' AND upv.downvote) as image_posts_downvote_count
FROM user_post_views upv JOIN
     posts p
     ON upv.post_id = p.id 
GROUP BY upv.user_id;

变化：

不要对联接进行类型转换！这肯定会阻碍优化器。
userstable好像没必要
不需要子查询。
FILTER 比条件聚合稍快。更重要的是，意图更加明确。

按 PostgreSQL 中多个内部连接的条件计数

Count by condition of multiple inner joins in PostgreSQL

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