Question

I want to clear specific row values back to null, I have a prototype for loop that I would like to use. However I am afraid that it will delete everything in the table. The database has columns: user, password, correct, wrong, and game1, game2, game3…..game16. I want to clear the columns that start with game, but nothing else. It seems simple to do, however I cannot seem to make it work. Can someone help me understand?

$vals=array();
$sql="DELETE "; 
for ($i=1; $i<=16; ++$i) {
  if (isset(game$i)) { continue; }
  if ($i != 1) {
   $sql .= ",";
  }
  $sql .= "game$i=:game$i";
  $vals[":game$i"]="game$i";
  "game$i FROM user WHERE user = * ";
}

$statement=$db->prepare($sql);
$statement->execute($vals);

Answer 1

Setting a value to NULL is an UPDATE, and different than removing the record from the database (DELETE)

To prevent having to dynamically create you SQL Statement, it looks like you can (and probably should) just write out the whole SQL Script.

UPDATE u
SET u.game1 = NULL
   , u.game2 = NULL
   , u.game3 = NULL
   , u.game4 = NULL
   , u.game5 = NULL
   , u.game6 = NULL
   , u.game7 = NULL
   , u.game8 = NULL
   , u.game9 = NULL
   , u.game10 = NULL
   , u.game11 = NULL
   , u.game12 = NULL
   , u.game13 = NULL
   , u.game14 = NULL
   , u.game15 = NULL
   , u.game16 = NULL
FROM user AS u

FROM user AS u makes an alias for user, so I can reference the table with the single character u. You see this happen when I specify the UPDATE u (using the alias). W3Schools probably does a better job explaning SQL Aliases than I will.

You do not need (and should not have) a WHERE clause if you want the UPDATE to affect all the users, this is implied by not having a WHERE