PHP Security - (int) vs FILTER_VALIDATE_INT

The difference is that a cast to int will always get you an int, which may or may not be the original value. E.g. (int)'foobar' results in the int 0. This makes it safe for most SQL purposes, but has nothing to do with the original value, and you won't even know it.

filter_var with FILTER_VALIDATE_INT tells you whether the value is an int, based on which you can make the decision to use it in an SQL query or display an error message to the user.