De beste manier om te controleren op bestaande gebruikers in de mySQL-database?

Gebruik de WHERE clausule om alleen rijen met de opgegeven gebruikersnaam te krijgen:

"SELECT * FROM user_list WHERE uname='".$server->real_escape_string($uname)."'"

Controleer vervolgens of de zoekopdracht resulteert in het selecteren van rijen (ofwel 0 of 1 rij) met MySQLi_Result::num_rows :

function createUser($uname,$pword) {
    $server->connect(DB_HOST,DB_USER,DB_PASS,DB_NAME);
    $result = $server->query("SELECT * FROM user_list WHERE uname='".$server->real_escape_string($uname)."'");
    if ($result->num_rows() === 0) {
        if ($server->query("INSERT INTO user_list (uname) VALUES ('".$server->real_escape_string($uname)."'")) {
            echo "User added Successfully";
        } else {
            echo "Error while adding user!";
        }
    } else {
        echo "User already exists!";
    }
}