Do not break your indexes — SARGability and WHERE clause anti-patterns

Wed, 25 Feb 2026 00:00:00 +0000

TL;DR

Applying a function to a column in the WHERE clause stops SQL Server from using the indexes on that column. Such a query is called non-SARGable. The result: an Index Scan, a full traversal, instead of an Index Seek, a direct lookup.

The most frequent culprits: COALESCE, ISNULL, CONVERT, YEAR(), LEFT(), TRIM() applied to the filtered columns.

The fix: move the logic to the value or the parameter side, never to the column side.

SARGability on Rudi Bruchez

Do not break your indexes — SARGability and WHERE clause anti-patterns