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Asked: 2026-05-26T15:30:14+00:00

I have a query which uses a complicated set of CASE statements, some nested,

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I have a query which uses a complicated set of CASE statements, some nested, some with a COALESCE of CASE statements, and it is a pain to manage.

The same basic logic applies to around 12 columns in the SELECT, and could be modularised and placed in a function – with benefits including consistency and ease of prototyping.

Will putting the logic into a function massively impede performance? Are functions inherently slower?

The SELECT Pulls from 5 tables each of around 100,000 rows, so performance is of some importance.

SQL Server 2005

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  1. Editorial Team

    Normally, selecting a result of a scalar function won’t hurt much, but filtering by it may easily cost hundreds of seconds (not necessarily though).

    If you need to filter by a scalar function result (WHERE col = dbo.scalar_function()), it often helps to make an inline table-valued function instead. It would return its value as the only row of the result table. You would then do inner join with the function result, effectively filtering by the returned value. This works because SQL Server is always able to unwind inline table-valued functions and inline them into the calling query.

    Note this trick won’t work if the function is a multi-step one. These cannot be unwound.

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