Problem with if() statement, comparing primary keys with trigger

Hi there,
I am relatively new to sql and I am not quite sure how to write this out, I hope you don't mind me asking. I am comparing emails in my database in an email table that has these fields. lngEmailPK, lngStudentFK, strAddress, and lngEmailValue. lngEmailValue is the value of their primary key, 1 if primary and 0 if not primary. I have the right idea I think, but maybe I am not implementing it correctly.
I want to do the following:

/*If they have multiple emails and more than one is primary - remove all primaries. Insert a non primary - make it a primary.
Insert a primary and they already have a primary - strip out and allow them to enter this one as the primary.*/

if(@lngEmailValue %2 = 1 and @lngEmailValue = +2)
delete from tblEmail
where lngEmailValue = 1 and @lngEmailValue = +2
select @@identity
set @lngEmailValue = -1

if(@lngEmailValue %2 = 0)
update tblEmail
set @lngEmailValue = @lngEmailValue + 1
where lngStudentFK = @lngStudentFK AND lngEmailValue %2 = 1

if(@lngEmailValue %2 = 1)
update tblEmail
set @lngEmailValue = lngEmailValue -1
where lngStudentFK = @lngStudentFK AND lngEmailValue %2 = 1 AND lngEmailPK = @lngEmailPK
select @@identity
set @lngEmailValue = 1

If you need my tables to reference, I will be more than happy to send them. Just let me know if you do. Thank you very much.

I'm not entirely understanding what you're needing/wanting to do.. FYI, the Primary key is:



As for email management, this part right here is confusing me terribly.. are you wanting to do this so that they can mark the messages read/unread? or deleted/not deleted? What are you needing to do? why are you comparing the emails to the database? to confirm if they have been picked up yet?