Mysql 在 1 个表上选择和排序

Question

我是 MySQL 新手。我有一个具有以下结构和数据的表:

CREATE TABLE posts
    (`id` int, `title` varchar(255), `post_id` int, `type` varchar(255) )
;

INSERT INTO posts
    (`id`, `title`, `post_id`, `type`)
VALUES
    (1, 'Hello', NULL, 'post'),
    (2, 'This is title', NULL, 'post'),
    (3, NULL, 1, 'like'),
    (4, NULL, 1, 'like'),
    (5, NULL, 2, 'like')
;

我想像这样选择和排序帖子:

1. 你好 => 2(喜欢)
2. 这是标题 => 1(赞)

Answer 1

您可以执行自连接，并根据喜欢的数量进行排序:

SELECT   id, cnt
FROM     (SELECT id, title
          FROM   posts
          WHERE  title IS NOT NULL) titles
JOIN     (SELECT   post_id, COUNT(*) AS cnt
          FROM     posts
          WHERE    type = 'like'
          GROUP BY post_id) likes ON titles.id = likes.post_id
ORDER BY cnt DESC