php - 为什么别名会导致我的查询在 phpMyAdmin 中失败？

Question

以下查询在我的 php 脚本中运行良好，但是当我在 phpMyAdmin 中运行它时(针对同一个数据库)，我没有得到任何结果(甚至没有“0 个结果”——它只是刷新页面)。

  SELECT comment, username, image, post_date, ((us.user_id != 22) AND

        ((SELECT read_date FROM
        bookmarks WHERE
        product_id=456029 AND
        user_id=22) < post_date)) AS
        new_comment FROM

        comments AS
        co, users AS
        us, flair WHERE co.product_id=456029 AND
        co.user_id=us.user_id AND
        flair_id=us.active_flair_id ORDER BY
        co.post_date ASC

我注意到如果我去掉别名，查询在 phpMyAdmin 中有效

SELECT comment, username, image, post_date, ((users.user_id != 22) AND

        ((SELECT read_date FROM
        bookmarks WHERE
        product_id=456029 AND
        user_id=22) < post_date)) AS
        new_comment FROM

        comments, users, flair WHERE comments.product_id=456029 AND
        comments.user_id=users.user_id AND
        flair_id=users.active_flair_id ORDER BY
        comments.post_date ASC

我很好奇为什么会这样。 (运行 phpMyAdmin - 2.11.9.5)

编辑:Richard 在 phpMyAdmin 中的以下重新表述有效。所以现在的难题是为什么一种公式有效而另一种公式无效(当它们在 php 脚本中执行时都工作正常)。

按照 Richard 的建议删除子查询的查询的最终形式:

SELECT c.comment AS 
COMMENT , username, image, DATE_FORMAT( c.post_date,  '%b %D, %Y' ) AS post_date, IF( (
(
b.read_date IS NULL
)
OR (
b.read_date < c.post_date
) ) , IF( c.user_id !=1, 1, 0 ) , 0
) AS new_comment
FROM comments c
INNER JOIN users u ON c.user_id = u.user_id
INNER JOIN flair f ON flair_id = u.active_flair_id
LEFT JOIN bookmarks b ON ( b.product_id = c.product_id
AND b.user_id =1 ) 
WHERE c.product_id =538968
ORDER BY c.post_date ASC 

Answer 1

你的问题很奇怪，我也不会接受...

   SELECT comment, username, image, post_date
        , (
              (users.user_id != 22) 
          AND (
                  (
                       SELECT read_date 
                         FROM bookmarks 
                        WHERE product_id=456029 
                          AND user_id=22
                  ) 
              < post_date)
         ) AS new_comment 
    FROM comments, users, flair 
   WHERE comments.product_id=456029 
     AND comments.user_id=users.user_id 
     AND flair_id=users.active_flair_id 
ORDER BY comments.post_date ASC

小改写:

     SELECT comment, username, image, post_date
          , (
                (u.user_id != 22) # What is this for? First you check if it is not user 22
            AND (
                    (
                       SELECT read_date 
                           FROM bookmarks 
                         WHERE product_id=456029 
                            AND user_id=22  # And now you check if it is
                    ) 
                < post_date)
           ) AS new_comment 
      FROM comments c
INNER JOIN users u ON c.user_id = u.user_id 
INNER JOIN flair f ON flair_id = u.active_flair_id 
     WHERE c.product_id = 456029 
  ORDER BY c.post_date ASC

此查询的目标是什么？这当然可以写得更好......

这个怎么样:

    SELECT c.comment, username, image, c.post_date
         , IF(b.read_date < c.post_date, 1, 0) AS new_comment 
      FROM comments c
INNER JOIN users u ON c.user_id = u.user_id 
INNER JOIN flair f ON flair_id = u.active_flair_id 
 LEFT JOIN bookmarks b ON (b.product_id = c.product_id AND b.user_id = u.user_id)
     WHERE c.product_id = 456029 
  ORDER BY c.post_date ASC

您的查询中没有理由使用子查询。