mysql - 使用 LEFT 连接的 LIMIT 行

Question

我有“发布”和“评论”表格。我想要选择最后 3 篇文章 和该文章的所有评论。目前我使用 2 个单独的语句:

SELECT p.* FROM post p ORDER BY p.date DESC LIMIT 3; // called 1
SELECT c.* FROM comment c WHERE c.post_id = :id; // called 3x time for each post.

是否可以将这些查询合并为一个？

Answer 1

您可以对帖子集使用子查询:

SELECT p.*
FROM (SELECT p.*
      FROM post p
      ORDER BY p.date DESC
      LIMIT 3
     ) p JOIN
     comment c
     ON c.post_id = p.id
ORDER BY p.id, c.id;