Question

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Find duplicate records in MySQL

I am a newbe trying to find duplicates in a database with this function:

function uni($field, $value) {
        $sql= "SELECT * FROM user WHERE ".$field." = '".$value."'";
        $result = $pdo->query($sql);
        $rows = $result->fetchAll(PDO::FETCH_COLUMN, 1);
        return count($rows);
    }

$username = $_POST['username']; 
$result = uni("username", $username);

…i am about to bang my head against something solid. For some reason the query won’t return a result and I dont know why.

Answer 1

Ok, so you’re using PDO, good. Your snippet is still wide open to injection attacks, though: you’re still passing raw user input to a query. Also, don’t use SELECT * if all you want is the number of rows that were found, and don’t FETCH the full result-set to count them!

function uni($field,$value)
{
    $db = new PDO();//make connection, which you don't seem to do
    //or (not so good approach):
    //global $db;
    //Best approach would be to pass the connection to the function, as an extra argument, though
    $stmt = $db->prepare('SELECT '.$field.' FROM user WHERE '.$field.' = :value');
    if ($stmt->execute(array(':value' => $value)))
    {
        return $stmt->rowCount();
    }
    //query failed, throw errors or something
}

Read the docs for more examples.
Anyway, your code, in full should look like this:

function uni($field,$value,$db)
{
    $stmt = $db->prepare('SELECT '.$field.' FROM user WHERE '.$field.' = :value');
    if ($stmt->execute(array(':value' => $value)))
    {
        return $stmt->rowCount();
    }
    return false;
}
$username = $_POST['username']; 
$result = uni('username', $username,$pdo);//<--pass connection