Can you reuse already determined calculations in select statements? e.g

If I have this valid select part of a statement to work out a distribution of events :

SELECT  
            SUM(CASE WHEN CreatedDate BETWEEN Dateadd(month, - 1, getdate()) AND getdate() THEN 1 ELSE 0 END) AS Period,             COUNT(LastClientCareCall.ContactId) AS NumberOfClients


I need to add a percentage calculation and my instinct is to append to the end something like ",100/NumberOfClients*Period as PercentageOfPeriod" but this is of course not possible.  I could obviously reuse all my formulas and make a very long winded "100/COUNT(LastClientCareCall.ContactId)*SUM(CASE WHEN CreatedDate BETWEEN Dateadd(month, - 1, getdate()) AND getdate() THEN 1 ELSE 0 END)" but wondered if there was a mechanism for using the output of the previously used alias's to achieve something more tidy?

Thanks in advance
dgloverukAsked:
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Jim HornMicrosoft SQL Server Data DudeCommented:
afaik nope, as the SELECT clause processes as a whole and not left-to-right where the left columns are retained in memory before the right ones are processed.  The main workaround would be to have your needed calculations in a subquery, and the ones that use them in a main query.   Something like..

SELECT a, b, the_count / the_sum as the_percent
FROM ( 
   SELECT a, b, COUNT(b) as the_count, SUM(b) as the_sum
   FROM some_table) one

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I'm not quite understanding your calculations, so if you can give a data mockup maybe I'll be able to provide custom SQL to match.

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dgloverukAuthor Commented:
Hi Jim,
That will be fine, I will nest the 1st query inside and then work with the alias names as you demonstrate.
Thank you!
Regards,
Jim HornMicrosoft SQL Server Data DudeCommented:
Thanks for the grade.  Good luck with your stuff.  -Jim
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