Question

How would I determine if a $_POST is null? I want to do an if/else based on whether an ID is submitted or not, to determine whether a record should be inserted into a MySQL database, or updated.

Would I use isset($_POST["ID"]) ?

Answer 1

There are several functions in php for this.

People use empty or isset for this purpose. Many use the one and dont think about the difference.

This example from the documentation shows clearly the difference.

$var = 0;

// Evaluates to true because $var is empty
if (empty($var)) {
    echo '$var is either 0, empty, or not set at all';
}

// Evaluates as true because $var is set
if (isset($var)) {
    echo '$var is set even though it is empty';
}

In this particular case, you should use empty and not isset, because the variable can be set, but empty.