T-SQL: How to Select Values in Value List that are NOT IN the Table?

Question

I have a list of e-mail addresses, some of them are in my table, some of them are not. I want to select all e-mails from that list and whether they are in the table or not.

Answer 1

When you do not want to have the emails in the list that are in the database you'll can do the following:

select    u.name
        , u.EMAIL
        , a.emailadres
        , case when a.emailadres is null then 'Not exists'
               else 'Exists'
          end as 'Existence'
from      users u
          left join (          select 'email1' as emailadres
                     union all select 'email2'
                     union all select 'email3') a
            on  a.emailadres = u.EMAIL)

this way you'll get a result like

name | email  | emailadres | existence
-----|--------|------------|----------
NULL | NULL   | a@b.com    | Not exists
Jan  | j@j.nl | j@j.nl     | Exists

Using the IN or EXISTS operators are more heavy then the left join in this case.

Good luck :)