PHP更优雅的方式来处理mysqli错误

Question

With pure PHP code (and not frameworks) is there a more elegant way to handle mysqli errors as shown below:

if (!mysqli_query($con, $sql)) {
            # Throw error so we can handle them
            echo mysqli_error($con);

            # handle a duplicate email
            if (strpos(mysqli_error($con), "email_UNIQUE") !== false ) {
                    $_SESSION["errors_found"] = true;
                    array_push($_SESSION["error_messages"], "Email given is already registered.");
            }

            # handle a duplicate username
            else if (strpos(mysqli_error($con), "username_UNIQUE") !== false ) {
                    $_SESSION["errors_found"] = true;
                    array_push($_SESSION["error_messages"], "Username is already taken.");
            }

            # handle any other sql query error...
           else {
                die("Database query error: " . mysqli_error($con));
            }
    }

Answer 1

First of all, I wouldn't call such a process "handling mysqli errors", but rather "user input validation".
And secondly, I wouldn't perform such a validation this way at all.

I've always been under impression that validating user input against database usually performed using SELECT queries, not INSERT ones.
It will not only make your application error-free, but also make it more flexible, allowing separate verifications for the AJAX-based registration for example.

As for the real mysqli errors - you really have to handle them, instead of just dying.
Most convenient yet easy way would be throwing an Exception:

if (!mysqli_query($con, $sql)) {
    throw new Exception(mysqli_error($con));
}

which will be properly handled according to site-wide error handling settings and also provide priceless trace log.