COUNT（*）在子查询中返回每一行，而不仅仅是那些特定的ID

Question

我试图通过子查询来计算与每个书签相关的标签和评论的数量。但是，它只是计算所有标签和评论。

SELECT 
    bookmarks.bookmark_id, 
    bookmarks.user_id, 
    DATE_FORMAT(bookmarks.creation, '%W %D of %M %Y, %H:%i') AS creation, 
    DATE_FORMAT(bookmarks.modification, '%W %D of %M %Y, %H:%i') AS modification, 
    bookmarks.url, 
    bookmarks.title, 
    bookmarks.snippet, 
    bookmarks.status, 
    (
     SELECT 
      COUNT(tags.tag) AS tags 
     FROM 
      tags 
     INNER JOIN 
      bookmarks 
     ON 
      (tags.bookmark_id = bookmarks.bookmark_id) 
     WHERE 
      (tags.user_id = '1') 
    ) AS tags, 
    (
     SELECT 
      COUNT(bookmarks_comments.comment) AS comments 
     FROM 
      bookmarks_comments 
     INNER JOIN 
      bookmarks 
     ON 
      (bookmarks_comments.bookmark_id = bookmarks.bookmark_id) 
     WHERE 
      (bookmarks_comments.user_id = '1') 
    ) AS comments 
FROM 
    bookmarks 
WHERE 
    (bookmarks.user_id = '1') 
GROUP BY bookmarks.bookmark_id 

也许是时间的晚了。我不知道。但我无法弄清楚。有任何想法吗？

Answer 1

您的子查询正在进行连接，因此它与外部查询不相关。这里是你想要的第一个：

(
    SELECT 
     COUNT(tags.tag) AS tags 
    FROM 
     tags 
    where 
     (tags.bookmark_id = bookmarks.bookmark_id) 
    and 
     (tags.user_id = '1') 
) AS tags, 

通知我删除了join。现在，当SQL看到bookmarks.bookmarks_id时，它将转到外部查询中的bookmarks表。

而你也有与comments相同的问题。