Visual Studio 2008 Case Expression using null

I'm trying to right a report that lets a user select either 'all values including null' or 'all values excluding null'. I placed a case expression in the where section. It doesn't work correctly for two reasons:

• I can't 开发者_开发问答pull the values of null and is not null at the same time.
• In both cases it ends up pulling all values including null for the first one and only null values for the second.

Where

((CASE WHEN @nullvalue = 1 THEN check_rtn_void_dte end is not null) OR (CASE WHEN @nullvalue = 2 THEN check_rtn_void_dte end is null))

Is there a operator I can use that will pull null and is not null in one statement? Also, why is the first case pulling all data including null values?

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Perhaps something like this would be simpler...

SELECT *
FROM MyTable
WHERE (@nullvalue = 2 OR check_rtn_void_dte IS NOT NULL)

That should pull out all results if @nullvalue = 2, or only non-NULL values if @nullvalue is something else.