check if a date exists within a grouped row and if it does then change column in sql

I have a database query that groups payments due into monthly values.

The problem I am facing now is that I can not see each individual payments to be able to make sure all are paid.

dp within the column is Date Paid.

If the date within the column is 0000-00-00 00:00:00 then no payment has been made.

Here is the query:

$monthlyQuery = $pdo->prepare("
SELECT SUM(net) AS net
     , MONTH(dd) AS month
     , YEAR(dd) AS year
     , dp 
  FROM sin WHERE cpo=:cpo 
   AND dd >= :dd1 
   AND dd <= :dd2 
 GROUP 
    BY month 
 ORDER 
    BY dd ASC
 ");
$monthlyQuery->execute(array(':cpo' => $fetch['cpo'], ':dd1' => $janDate, ':dd2' => $decDate));
$monthlyQueryNum = $monthlyQuery->rowCount();

is there a way to check each dp column before the row is grouped and if at any point the date is 0000-00-00 00:00:00 then make all dates for that group 0000-00-00 00:00:00

I was thinking of doing a CASE WHEN THEN but the logic doesn’t seem to work for me.

Thanks

check if a date exists within a grouped row and if it does then change column in sql