PHP MySQL - ON DUPLICATE KEY UPDATE

["Phillip Terry" <pterry@xxxxxxxxxxx>]

Is there an easy way to overwrite a row (e.g. using replace) if a duplicate key already exists?

For instance, is there something like ON DUPLICATE KEY REPLACE (as opposed to UPDATE)?

Or do I have to:

key_exists = query database for key
if (key_exists){
    REPLACE...
}
else{
    INSERT...
}

Thank you!

Phillip