Question

Would someone be able to give me a MySQL relation query for looking up a column value of a table based off of another value of the same table?

For instance, I have a table with 4 columns (id, name, email, password). How could I look up the the value of the “id” column of a certain user based off of their email in the “email” column and store the result (id) in a variable?

Here’s the session() controller function

function userIsLoggedIn()
{
    if (isset($_POST['action']) and $_POST['action'] == 'login')
    {
        if (!isset($_POST['email']) or $_POST['email'] == '' or
            !isset($_POST['password']) or $_POST['password'] == '')
        {
            $GLOBALS['loginError'] = 'Please fill in both fields';
            return FALSE;
        }

        $password = md5($_POST['password'] . 'chainfire db');

        if (databaseContainsAuthor($_POST['email'], $password))
        {
            session_start();
            $_SESSION['loggedIn'] = TRUE;
            $_SESSION['email'] = $_POST['email'];
            $_SESSION['password'] = $password;
            $_SESSION['authorid'] = $author;
            return TRUE;
        }
        else
        {
            session_start();
            unset($_SESSION['loggedIn']);
            unset($_SESSION['email']);
            unset($_SESSION['password']);
            unset($_SESSION['authorid']);
            $GLOBALS['loginError'] =
                    'The specified email address or password was incorrect.';
            return FALSE;
        }
    }

I’ve tried

SELECT id FROM article WHERE email='$email' 

Is there a more efficient way to do it? I’m also not totally sure how to store the result of the query in the $author session variable.

Thanks in advance.

Answer 1

Your query is perfect (with the proviso that you are sanitising the $email variable – see the tale of Little Bobby Tables).

SELECT id FROM article WHERE email='$email'

And to perform that query and set the variable $author to the returned value is simply:

$author = 0;
if( ( $idFromEmail = @mysql_query( "SELECT id FROM article WHERE email='".mysql_real_escape_string( $email )."'" ) )
    && mysql_num_rows( $idFromEmail )==1
    && ( $r = mysql_fetch_assoc( $idFromEmail ) ) ){
    $author = $r['id'];
}

Rewritten in long form, if the above is too complex to follow:

$author = 0;
if( !( $idFromEmail = @mysql_query( "SELECT id FROM article WHERE email='".mysql_real_escape_string( $email )."'" ) ){
  // SQL Query Failed
}elseif( mysql_num_rows( $idFromEmail )!=1 ){
  // More than, or less than, one row returned
}else{
  $r = mysql_fetch_assoc( $idFromEmail );
  $author = $r['id'];
}