Question

I am trying to do something I’ve done a million times and it’s not working, can anyone tell me why?

I have a table for people who sent in resumes, and it has their email address in it…

I want to find out if any of these people have NOT signed up on the web site. The aspnet_Membership table has all the people who ARE signed up on the web site.

There are 9472 job seekers, with unique email addresses.

This query produces 1793 results:

select j.email from jobseeker j join aspnet_Membership m on j.email = m.email 

This suggests that there should be 7679 (9472-1793) emails of people who are not signed up on the web site. Since 1793 of them DID match, I would expect the rest of them DON’T match… but when I do the query for that, I get nothing!

Why is this query giving me nothing???

select j.email  from jobseeker j where j.email not in (select email from aspnet_Membership) 

I don’t know how that could be not working – it basically says ‘show me all the emails which are IN the jobseeker table, but NOT IN the aspnet_Membership table…

Answer 1

We had a very similar problem recently where the subquery was returning null values sometimes. Then, the in statement treats null in a weird way, I think always matching the value, so if you change your query to:

select j.email  from jobseeker j where j.email not in (select email from aspnet_Membership                       where email is not null) 

it may work….