PDO rowcount返回值

I am using PHP's PDO (with mysql server) to update a table. Something similar to the query:

UPDATE  game g
SET     g.some_field=1
WHERE   g.game_id=:game_id AND g.is_finished=1
AND     (g.player1=:player_id OR g.player2=:player_id)
LIMIT   1

executed like this:

$psResult = $ps->execute();
if( !$psResult ){
    // database error
} else if( $ps->rowCount() <= 0 ){
    // no row was updated.
}

Now the else-if statement that does the rowCount() check can be 0 when:

• There is no record with a game id equal to :game_id which has is_finished set to 1 and has :player_id as either player1 or player2.
• There was such a record but the some_field was already set to 1.

I need to distinguish these in order to return a correct error/value. For example return true if the field was set to 1 or already had 1 and return false if no record was matched.

How can I do this? Is there another way then doing an extra query?