Question

I’ve got a SQL table (Email_Campaigns) with a master list of campaigns we’ve run:

Name            DateSent
Campaign01    01/01/2011
Campaign02    01/15/2011
..
Campaign40    10/01/2011

I’ve got a list of customers (Email_Received) with their membership numbers and the campaigns they’ve received:

PK    MembershipNo    CampaignName
1           123456      Campaign01
2           123456      Campaign02
3           987654      Campaign05
4           111111      Campaign10

I’ve also got a master list of customer MembershipNo’s (Customers)

Question: How do I write a query to list each campaign and count the number of customers who DID NOT receive that e-mail? For example (‘Received’ column is only shown here for reference and isn’t imperative as I know how to calculate that):

Name          Received    DidNotReceive
Campaign01        1000             9000
Campaign02        3000             7000
..
Campaign40         100             9900

Answer 1

Here’s one standard SQL way to write this:

SELECT ec.Name, count(c.MembershipNo) AS DidNotReceive
  FROM Customers AS c
     , Email_Campaigns AS ec
 WHERE NOT EXISTS (
    SELECT 1
      FROM Email_Received AS r
     WHERE er.CampaignName = ec.CampaignName
       AND er.MembershipNo = c.MembershipNo)
 GROUP BY ec.Name
 ORDER BY ec.Name;