How to Calculate the Sum of Cash Values within the Last Month in SQL?

Calculating Sum with Conditional Filtering in SQL

When dealing with large SQL statements, it is often necessary to calculate summary values. However, sometimes it is required to only consider a subset of the data based on a specific condition. This article explores how to modify an existing statement to calculate the sum of cash values for unique transaction IDs, but only for those with a valuedate within the last month.

Problem:

To calculate the total cash for each transaction ID within a complex SQL statement, the following code is used:

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

However, the aim is to modify this statement to only sum cash values that have a valuedate within the last month.

Solution:

The revised code should replace the original CASE expression with the following:

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

Explanation:

The CASE expression in your original code was using incorrect syntax. The SEARCH CASE syntax is required in this case because a Boolean expression is being evaluated to determine the result:

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

In the revised code, the CASE expression checks if the ValueDate is greater than the @startMonthDate. If it is, the cash amount is included in the calculation; otherwise, it is replaced with 0. This ensures that only cash values within the last month are considered.

Performance Considerations:

If performance becomes an issue, it is recommended to consider using a JOIN and GROUP BY instead of a dependent subquery. This may improve the execution speed of the statement.

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