is_unique in Form Validation on UPDATE

for me, if i have to check differents values on UPDATE or INSERT, I create 2 validation rules.

// user_validation_insert => 'email' => 'valid_email|is_unique[user.email]'

// user_validation_update => 'email' => 'valid_email'


something like that

But what if you changed your email when editing? It still has to be unique, so the check has to be run, otherwise you could change it to an email which already exists.