Question

I have the following function

function availableChatRoom($topic_id){
$max_rooms = 2;
$max_users = 2;

$sqli = "SELECT COUNT(DISTINCT room_num) AS numRooms FROM forum_chat WHERE topic_id = '$topic_id'";
$num_rooms = queryColumnVal($sqli, "numRooms");

$sqlii = "SELECT room_num, COUNT(user_id) AS numUsers FROM forum_chat 
          WHERE topic_id = '$topic_id' AND (status = 'online' AND status = 'offline') AND chat_msg = ''
          GROUP BY room_num
          HAVING numUsers < $max_users ORDER BY msg_date";

$num_rooms_with_spaces = mysqlNumRows($sqlii, "room_num");
queryColumnVal($sqlii, "room_num");

if($num_rooms == 0){
    return 1;
}
elseif($num_rooms <= $max_rooms){

    if($num_rooms_with_spaces == 0){
        return $num_rooms + 1;
    }
    else{
        return queryColumnVal($sqlii, "room_num");
    }
}
else{
    return "none";
}   

}

the idea is for the function to return a chat room number with space.
-Every time a user joins the room, a line with no msg is inserted with status online
-Every time a user leaves the room a line with no msg is inserted with status offline
I am now trying to write a function which checks if there are any spare rooms for each topic
The idea is to select the room_num where the number of users who have logged in but not logged out is less than the maximum chatter per room.
Can someone help me with my $sqlii.

Thanks

Answer 1

There are several errors in your query:

• (status = 'online' AND status = 'offline')

This asserts that your query wil return no now at all. Use: (status = 'online' OR status = 'offline') or the equivalent (status IN ('online', 'offline'))

• COUNT(user_id)

This does not count the difference of online minus offline users. Correct the logic.

• ORDER BY msg_date

In GROUP BY queries, it’s not good to use non-aggregate column, at the HAVING, SELECT or ORDER BY clauses, despite that MySQL allows it. Unless that column depends on the grouping expression. Since msg_date obviously does not depend on room_num, you should replace that with an aggregate function:

ORDER BY MAX(msg_date) or ORDER BY MIN(msg_date)

---

$sqlii = "
   SELECT room_num, 
          COUNT(CASE WHEN status = 'online' THEN 1 END) 
            - COUNT(CASE WHEN status = 'offline' THEN 1 END) 
          AS numUsers 
   FROM forum_chat 
   WHERE topic_id = '$topic_id' 
     AND status IN ('online', 'offline')
     AND chat_msg = ''
   GROUP BY room_num
   HAVING COUNT(CASE WHEN status = 'online' THEN 1 END) 
          - COUNT(CASE WHEN status = 'offline' THEN 1 END) 
          < $max_users 
   ORDER BY MAX(msg_date)
     ";