# General Guidelines for Index Optimization > [!Note] > `Effective index design depends on ordering key columns for high-selectivity filters, prioritizing equality predicates, strategically including additional columns to cover queries, and avoiding functions in predicates to enable efficient index usage.` When designing nonclustered indexes, the sequence of key columns should reflect how often each column appears in highly selective WHERE clauses—placing the most selective column first empowers the optimizer to perform precise seeks. Predicates that use equality on the leading key allow direct jumps in the B-Tree, whereas range predicates (>, <, BETWEEN) diminish seek efficiency by requiring broader scans. Including nonessential columns via the INCLUDE clause can transform an index into a covering structure—eliminating lookups to the base table without inflating the B-Tree’s internal nodes—so long as only the columns needed for the SELECT list are added. Finally, wrapping key columns in functions prevents the optimizer from leveraging indexes altogether; if transformations are unavoidable, consider creating computed columns and indexing them directly. Below is a concise tabular summary of these recommendations: |**Tip**|**Description**| |---|---| |**1. Order Columns by Selectivity**|Place the column with the highest selectivity (most filtered) first in the key definition to enable precise seeks and narrow down the search space.| |**2. Favor Equality on Leading Key**|Equality predicates on the first key column permit direct B-Tree navigation; range predicates degrade index seek efficiency by forcing broader scans.| |**3. Include Only Necessary Columns**|Use INCLUDE to add only those columns in the SELECT list—covering queries without enlarging the B-Tree or increasing page-split risk.| |**4. Avoid Functions in Predicates**|Transformations on indexed columns block efficient index use; if needed, index a computed column rather than wrapping the predicate in a function.| --- ## ## References - Korotkevitch, D. (2022). _SQL Server advanced troubleshooting and performance tuning: Best practices and techniques_. O’Reilly Media. - Nevarez, B. (2022). _SQL Server query tuning and optimization: Optimize Microsoft SQL Server 2022 queries and applications_. Packt Publishing.