Easiest way, make the column in the database unique and then just handle error, or during form validation you can execute for example:
If the value is more than 0 then record with provided emailID is already in database.
There are more efficient queries than above but i dont know what kind of database are you using. Still i am not sure if it is what you asked, as your question is really difficult to understand.
Joined: Sep 28, 2011
Yeah, your understanding is correct.
subject: User registration page validation after clicking submit.