Question

我使用嵌套的MySQL查询来获取用户帖子，当我在子查询中放入SQL_CALC_FOUND_ROWS时，MySQL返回错误：Incorrect usage/placement of 'SQL_CALC_FOUND_ROWS'

查询是：

SELECT inner_table.*
  , users.username as last_username
  , posts.date_added as last_date_added
  , users.user_id as last_user_id
  , posts.date_added as last_post_date 
FROM (
    SELECT SQL_CALC_FOUND_ROWS topics.topic_id
      , topics.date_added
      , topics.title
      , topics.user_id
      , MAX(posts.post_id) as last_post
      , posts.user_id as post_user_id
      , users.username
      , topics.previews
      , topics.fcat_id
      , topics.is_important
      , topics.is_locked
      , topics.lastpost_time
      , (SELECT COUNT(*) FROM posts WHERE posts.topic_id=topics.topic_id) as posts_cnt
    FROM topics
    LEFT JOIN users ON (users.user_id = topics.user_id)
    LEFT JOIN posts ON (topics.topic_id = posts.topic_id)
    WHERE topics.user_id = ".$this->session->getSession("user_data", "user_id")."
    OR ".$this->session->getSession("user_data", "user_id")."
    IN (
      SELECT DISTINCT user_id
      FROM posts
      WHERE posts.topic_id = topics.topic_id
    )
    GROUP BY topics.topic_id
    ORDER BY topics.lastpost_time DESC
    LIMIT ".$limit * $page.", ".$limit."
    ) as inner_table
LEFT JOIN `posts` ON (posts.post_id=inner_table.last_post)
LEFT JOIN `users` ON (users.user_id=posts.user_id)
ORDER BY inner_table.lastpost_time DESC

Answer 1

我认为内部查询不允许SQL_CALC_FOUND_ROWS 改为使用外部查询。

SELECT SQL_CALC_FOUND_ROWS inner_table.*
  ....

你最后一行也有错误：

ORDER BY inner_table.lastpost_time DES

将其替换为：

ORDER BY inner_table.lastpost_time DESC

<强>更新

回应您的评论以下的解决方法。

将内部选择输出到临时表。

使用这样的代码：

/* do this once*/
CREATE TABLE `temp_table` LIKE SELECT topics.topic_id
      , topics.date_added ....

/*do this for every query*/
DELETE FROM temp_table WHERE temp_table.topic_id <> 0;
INSERT INTO temp_table SELECT topics.topic_id
  , topics.date_added
  , topics.title
.... /*!! without the limit clause !!*/
SELECT count(*) as rowcount FROM temp_table;

/*then use the temp_table in place of the inner select*/

SELECT inner_table.*
 , users.username as last_username
  , posts.date_added as last_date_added
  , users.user_id as last_user_id
  , posts.date_added as last_post_date 
FROM temp_table .....
LIMIT ....

使用SQL_CALC_FOUND_ROWS也无法在INSERT .. SELECT上工作，但上面的代码是一种解决方法，你当然可以单独使用LIMIT 1运行内部查询，以使其尽可能快

SQL_CALC_FOUND_ROWS返回错误

1 个答案: