PHP - detect mysql update/insertion failure due to violated unique constraint

Question

This is kind of similar to this question:

PHP MySQL INSERT fails due to unique constraint

but I have a different twist. Let\'s say I have a table with only

Answer 1

If you know some SQL, try this solution (tested)

$username = "John";
$stmt = $pdo->prepare("
    INSERT INTO users (
        username
    ) SELECT * FROM (
        SELECT :username
    ) AS compare
    WHERE NOT EXISTS (
        SELECT username 
        FROM users 
        WHERE username = :username
    ) LIMIT 1;
");
$stmt->bindParam(":username", $username);
if ($stmt->execute()) {
    if ($stmt->rowCount() == 0) {
        echo "Dublicate Username, ".$username." already exists.";
    } else {
        echo $username." not in use yet.";
    }
}