Question

I have a users table and a users_banlist table.

On my registration form i want to check all in one query whether the username someone entered on form exists in the users table and see if it also exists on the users_banlist table.

I can do them on there own in individual queries but would rather do it all in one.

Here is what I got, but even though I enter a username that is taken it does not tell me it’s already taken.

$stmt = $dbh->prepare("
SELECT
  users.user_login,
  users_banlist.user_banlist
FROM
  users ,
  users_banlist
WHERE
  users.user_login = ? OR
  users_banlist.user_banlist = ?");

// checker if username exists in users table or users_banlist table
$stmt->execute(array($username, $username));

if ( $stmt->rowCount() > 0 ) {
    $error[] = 'Username already taken';
}

Basically I think it is something to do with the execute or rowCount(), could anyone tell me where I am going wrong? Being new to pdo I’m finding it a little confusing at the moment.

Answer 1

You could use the query

SELECT
  users.user_login
FROM
 users 
WHERE
  users.user_login = ? 
UNION ALL
SELECT
  users_banlist.user_banlist
FROM
  users_banlist
WHERE
  users_banlist.user_banlist = ?

and then proceed as normal. What you were using is a CROSS JOIN which returns the cartesian product that produce rows which combine each row from the first table with each row from the second table. If one of those tables returns 0 rows you get 0 results