I have a simple form that has one field:

email

And my forms action is: email.php

In email.php, i just insert the email address to a table called:

site

and a database called:

petesmc_misc



What i want to know is, using PHP how can i check for a duplicate value in the table before trying to insert. If i insert then the user would get the message:

You could not be added: Duplicate value, "test@test.com" for Key 1

Is there a way i can check first then say if it is duplicate?

Thanx