PHP and Mysql to much adding data

i'm generating random team array.All players are stored in DB without team. I need to assign 20 players from database to a team and get their info into array. I wrote the code, but somehow code assigns 60 players instead of 20 in database. Where did I went wrong?

 $Team = array();
   $i=0;
   while($i < 20)
   {
     $rand = rand(1,100);
     $sql = $con->query("SELECT * FROM players where id='$rand'");
     if($sql->num_rows > 0)
     {
       $data = $sql->fetch_array();
       if($data['teamid'] == NULL)
       {
         $con->query("UPDATE players SET teamid='$teamid' WHERE id='$rand'");
         $Team [$i]['name'] = $data['name'];
         $Team [$i]['surfname'] = $data['surfname'];
         $Team [$i]['rating'] = $data['rating'];
         $Team [$i]['position'] = $data['position'];
         $i++;
       }
     }
   }