PHP PDO - Using MySQL Variables

Question

I'm trying to run a query in PHP using PDO. The query has some variables at the top to determine a rank, except the when using the SET @var in the $sql, it returns an empty rowset. If I remove the offending SQL however, it returns fine.

I don't want to return @prev_value, @rank_count or @rank_increasing in my script, only the rank it creates in the SELECT.

Can you let me know what I am doing wrong please?

Thanks

    $sql = "
    SET @prev_value = NULL;
    SET @rank_count = 0;
    SET @rank_increasing = 0;
    SELECT a.*
         , @rank_increasing := @rank_increasing + 1 AS row_num
         , CASE
           WHEN @prev_value = score 
              THEN @rank_count
           WHEN @prev_value := score 
              THEN @rank_count := @rank_increasing
           END AS rank
      FROM ( 
           -- INLINE VIEW --
           ) a
    ";
    try {
        $sth = $dbh->prepare($sql);
        $sth->execute(array($var1, $var2));
        return $sth->fetchAll(PDO::FETCH_ASSOC);
    } catch (Exception $e) {
        return $e;
    }

Answer 1

Found the solution here: https://stackoverflow.com/a/4685040/1266457

Thank you :)

To fix:

// Prepare and execute the variables first
$sql = "
SET @prev_value = NULL;
SET @rank_count = 0;
SET @rank_increasing = 0;
";
$sth = $dbh->prepare($sql);
$sth->execute();

// Run the main query
$sql = "
SELECT a.*
     , @rank_increasing := @rank_increasing + 1 AS row_num
     , CASE
       WHEN @prev_value = score 
          THEN @rank_count
       WHEN @prev_value := score 
          THEN @rank_count := @rank_increasing
       END AS rank
  FROM ( 
       -- INLINE VIEW --
       ) a
"; ...