Detect mysql update/insertion failure due to violated unique constraint

Now that it’s the year 2015, there are very few reasons not to be using PHP’s PDO implementation.

The proper, modern, “OO” method for detecting and handling an insertion failure due to a key constraint violation is as follows:

try {
    //PDO query execution goes here.
}
catch (\PDOException $e) {
    if ($e->errorInfo[1] == 1062) {
        //The INSERT query failed due to a key constraint violation.
    }
}

The PDOException object has a lot more to say about the specific nature of the error, too (more detail than one could possibly ever want or need, seemingly).