SQL sum with condition

Question

I currently have a large SQL statement which i add the following line to in order to get the total cash for each transaction ID (which are unique):

select sum(cash) from Table a where a.branch = p.branch 
and a.transID = p.transID) TotalCash

and i now need to do the same but only total the cash values that have a valuedate within the last month, so i have something like this:

select sum(CASE ValueDate WHEN > @startMonthDate THEN cash ELSE NULL END) 
from Table a where a.branch = p.branch and a.transID = p.transID) TotalMonthCash

Sorry that I dont have the whole statement, but it is really long and specific to the context of the stored procedure but was hoping someone would know what i mean?

Answer 1

Try this instead:

SUM(CASE WHEN ValueDate > @startMonthDate THEN cash ELSE 0 END)

Explanation

Your CASE expression has incorrect syntax. It seems you are confusing the simple CASE expression syntax with the searched CASE expression syntax. See the documentation for CASE:

The CASE expression has two formats:

• The simple CASE expression compares an expression to a set of simple expressions to determine the result.
• The searched CASE expression evaluates a set of Boolean expressions to determine the result.

You want the searched CASE expression syntax:

CASE
     WHEN Boolean_expression THEN result_expression [ ...n ] 
     [ ELSE else_result_expression ] 
END

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As a side note, if performance is an issue you may find that this expression runs more quickly if you rewrite using a JOIN and GROUP BY instead of using a dependent subquery.