There really is no need for the ISNULL checks here. NULL is not in any of those value either. All the ISNULL check does here is makes it a nonSARGable predicate.
AND a.col1 NOT IN ('abc', 'def', 'ghi')
or (d.col2 is null or d.col2 NOT IN ('abc', 'def', 'ghi'))
I have to agree with Luis thought that without some clarification it is hard to know what you want here.
_______________________________________________________________
Need help? Help us help you.
Read the article at http://www.sqlservercentral.com/articles/Best+Practices/61537/ for best practices on asking questions.
Need to split a string? Try Jeff Modens splitter http://www.sqlservercentral.com/articles/Tally+Table/72993/.
Cross Tabs and Pivots, Part 1 – Converting Rows to Columns - http://www.sqlservercentral.com/articles/T-SQL/63681/
Cross Tabs and Pivots, Part 2 - Dynamic Cross Tabs - http://www.sqlservercentral.com/articles/Crosstab/65048/
Understanding and Using APPLY (Part 1) - http://www.sqlservercentral.com/articles/APPLY/69953/
Understanding and Using APPLY (Part 2) - http://www.sqlservercentral.com/articles/APPLY/69954/