PHP duplicate staffID

Question

• staff table
  

• code

  <?php
   //db configuration
   $q = "select * from staff";
   $r = mysqli_query($dbc, $q);
   $num_rows = mysqli_num_rows($r);
  
   $staffID = array();
   while($row = mysqli_fetch_array($r, MYSQLI_ASSOC))
   {
       $staffID[] = $row['staffID'];
   }
  
   for($i = 0; $i < $num_rows; $i++)
   {
       if($staffID[$i] == $staffID[$i+1])
       {
           $remark = "Not OK. Multiple staff ID selected.";
           $i++;
       }
       else
       {  
           $remark = "OK.";
       }
       $data[$i] = $staffID[$i].','.$remark.'<br />';
  }
  
  $list = array($data);
  print_r($list);
  ?>
  

• From above code, I want to check whether the staffID got duplicate.

• Expected output
  0001, OK.
  0002, Not OK. Multiple staffID.
  0003, OK.
  0004, OK.
  

• However, I get another error as below:
  Undefined offset: 5 in play.php on line X.
  How do I solve it?

Answer 1

By performing the correct query in the first place.

SELECT staffID
  FROM staff
  GROUP BY staffID
  HAVING COUNT(staffID) > 1

Or if you need to know about all staff IDs:

SELECT staffID, COUNT(staffID) as qty
  FROM staff
  GROUP BY staffID