Question

Im trying to run this query to Update member points When the member points equals the max value? to set the winner prize… but im getting this error.. thanks

Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘WHERE a.points = max(a.points) AND b.event_id = 4’ at line 4

    $sql="

    UPDATE engine4_event_membership a
    INNER JOIN engine4_event_events b ON b.event_id = a.resource_id
    SET a.points = a.points + case b.prize 
    WHERE a.points = max(a.points) AND b.event_id = '{$this->event->getIdentity()}';

    ";

Answer 1

If I’m understanding the data structure correctly, you can do this with a correlated subquery in the WHERE clause.

You are updating the membership table where resource_id is the input identity. You are looking for record(s) that have the maximum points. The following should do this:

UPDATE engine4_event_membership a join
       engine4_event_events b
       on b.event_id = a.resource_id
    SET a.points = a.points + b.prize 
    WHERE a.resource_id = '{$this->event->getIdentity()}' and
          a.points = (select max(a2.points)
                      from engine4_event_membership a2
                      where a2.resource_id a.resource_id
                     )

This will probably get the same MySQL error. So, the WHERE clause needs to be moved to the joins:

UPDATE engine4_event_membership a join
       engine4_event_events b
       on b.event_id = a.resource_id join
       (select resource_id, max(points) as maxpoints
        from engine4_event_membership
        group by resource_id
       ) amax
       on a.resource_id = amax.resource_id and
          a.points = amax.points
    SET a.points = a.points + b.prize 
    WHERE a.resource_id = '{$this->event->getIdentity()}'

The inability to use the target table in a correlated subquery is a limitation in MySQL.