problem in counting two fields in one query

Question

hey

guys i need to count new private messages and old one from a table

so first thing come to mind is using mysql_num_rows and easy thing to do

  // check new pms
  $user_id  = $userinfo['user_id'];
  $sql = "SELECT author_id  FROM bb3privmsgs_to WHERE user_id='$user_id' AND (pm_new='1' OR  pm_unread='1')";
  $result = $db->sql_query($sql) ;
  $new_pms = $db->sql_numrows($result);
  $db->sql_freeresult($result);

  // check old pms
  $sql = "SELECT author_id  FROM bb3privmsgs_to WHERE user_id='$user_id' AND (pm_new='0' OR  pm_unread='0')";
  $result = $db->sql_query($sql) ;
  $old_pms = $db->sql_numrows($result);
  $db->sql_freeresult($result);

but how can i count these two fields just in one statement and shorter lines ?~

Answer 1

Use this query instead:

SELECT SUM(CASE WHEN pm_new = '1' OR pm_unread = '1' THEN 1 ELSE 0 END) AS new_pms,
       SUM(CASE WHEN pm_new = '0' OR pm_unread = '0' THEN 1 ELSE 0 END) AS old_pms
  FROM bb3privmsgs_to
 WHERE user_id='$user_id'

Here's a MySQL-specific version that reads more cleanly:

SELECT COUNT(IF(pm_new = '1' OR pm_unread = '1', 1, NULL)) AS new_pms,
       COUNT(IF(pm_new = '0' OR pm_unread = '0', 1, NULL)) AS old_pms
  FROM bb3privmsgs_to
 WHERE user_id='$user_id'

Answer 2

In SQL Server, you can do something like this:

SELECT 
   SUM(CASE WHEN pm_new='1' OR  pm_unread='1' THEN 1 ELSE 0 END),
   SUM(CASE WHEN pm_new='0' OR  pm_unread='0' THEN 1 ELSE 0 END) 
FROM 
   bb3privmsgs_to WHERE user_id='$user_id'

I'll suppose you can do about the same thing in mySql, let me get back to you on the details...

Answer 3

MySQL will cast comparisons to 1 or 0. You can use SUM() to add up the portion of the WHERE clause you were trying to count results for.

This is a (MySQL specific) shorter alternative to the CASE WHEN examples.

SELECT 
  SUM(pm_new='1' OR pm_unread='1') as new_pms, 
  SUM(pm_new='0' OR pm_unread='0') as old_pms
FROM bb3privmsgs_to
WHERE user_id='$userid'

Answer 4

As a lazy alternative to some of the other suggestions:

SELECT SUM(newPMS) AS newPMS,
       SUM(oldPMS) AS oldPMS
  FROM ( SELECT COUNT(author_id) AS newPMS,
                0 AS oldPMS
           FROM bb3privmsgs_to
          WHERE user_id='$user_id'
            AND (pm_new='1' OR pm_unread='1')
         UNION
         SELECT 0 AS newPMS
                COUNT(author_id) AS oldPMS
           FROM bb3privmsgs_to
          WHERE user_id='$user_id'
            AND (pm_new='0' OR pm_unread='0')
       )