查找最近n个帖子中的用户帖子数

Question

I'm trying to find the most efficient way to find the number of posts by user in the last n rows of table .. I've tried

$db->query_first("SELECT COUNT(*) AS
user_recent_posts FROM " . TABLE_PREFIX . "post WHERE userid = $userid
AND threadid = '" . $threadinfo['threadid'] . "' AND visible = '1'
ORDER BY dateline DESC LIMIT 10" );

I'm trying to get the user posts in the last 10 posts in thread .. but this obviously returns last 10 posts by user regardless if they were in last 10 posts or not

Answer 1

Use a subselect to first get the n rows and then count the ones from your user:

$db->query_first("
  SELECT COUNT(b.*) AS user_recent_posts 
  FROM (
    SELECT a.* 
    FROM " . TABLE_PREFIX . "post a
    AND a.threadid = '" . $threadinfo['threadid'] . "' AND a.visible = '1'
    ORDER BY a.dateline DESC LIMIT 10) b
  WHERE b.userid = $userid" );