SQL Server › User Defined Functions

How would you design a set of reusable functions for a data warehouse to standardize common calculations like currency conversion or fiscal period determination?

Advanced

Answer

You would create inline table valued functions where possible for best performance, carefully name and document each function's purpose and parameters, centralize business logic like fiscal year boundaries into these functions rather than duplicating it across many reports, and thoroughly test them against edge cases like currency conversion rates that change over time.

CREATE FUNCTION dbo.GetFiscalYear (@Date DATE)
RETURNS INT
AS
BEGIN
  RETURN CASE WHEN MONTH(@Date) >= 4 THEN YEAR(@Date) ELSE YEAR(@Date) - 1 END;
END;

Real-world example A data warehouse team builds a standardized fiscal year calculation function used consistently across dozens of financial reports, eliminating inconsistent fiscal year logic that had previously been scattered and duplicated throughout different reports.

Common follow-ups: How do you handle a business rule, like fiscal year boundaries, that might change in the future?;What documentation practices help other developers understand and correctly use these shared functions?

Data Types & Schema Design;Views