query including an IF statement

I want my query to using a IF statement, identify; if the current num_unmarked will become 0 afte开发者_如何学Gor this update, then also set is final to 'YES'.

so here is my query:

 $sql = "UPDATE results_tb 
                    SET 
                        num_unmarked = num_unmarked - 1,
                        is_final=IF( num_unmarked-1=0, 'YES', is_final ),
                        score = score + $awarded
                    WHERE 
                        user_id = $student 
                    AND 
                        test_id = $test 
            ";

what is actually happening is, the query runs, num_unmarked decrements and score is updated however even if num_unmarked is 1 (not 0) it still sets is_final to 'YES'.

could somebody tell me what I am doing wrong please or enlighten me to a better way? (i am nooby :D)

thanks,

The updates are processed sequentially in MySql, so the update to num_unmarked occurs before the IF statement, and the IF statement uses the newly updated value. So you actually want to use the value as if it has already been updated, i.e., compare it directly to 0:

is_final = IF(num_unmarked=0, 'YES', is_final),