HOW TO CHECK THE EMIL ADDRESS EXIST IN THE DATABASE OR NOT

if your question is to just check if an email address exist then you can write something like
IF Exists(Select 1 from table where emailaddress = @address)
Begin
-----
End

if you just want to query and find out then you might have to check the count number of records
select count(1) from table where emailaddress = @address

If you have any specific requirement, let me know.