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From: "Bob Barrows" <reb01501@NOSPAMyahoo.com>
Newsgroups: comp.databases.ms-sqlserver,microsoft.public.sqlserver.programming
Subject: Re: SQL help again
Date: Sun, 2 Oct 2011 13:06:56 -0400
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Phil Hunt wrote:
> I tried
> CASE EventID when NULL then 1 else 0 end
>
> It always return 0, why ?
>
>
Because the way you have the statement structured is causing an equality 
comparison to be performed, the result of which will always be false. You 
have to structure it like:

CASE when  EventID IS NULL then 1 else 0 end

To answer your original question, you can subtract the result of 
count(distinct column_name) from count(*):

select count(*) - count(distinct eventid) as null_eventids