# Query Optimization and Indexing Hub > [!NOTE] > Central index for all **SQL Server query-optimization and indexing** notes. Topics are grouped by focus area—architecture, indexing, access patterns, joins & aggregates, and statistics—so you can jump straight to what you need. --- ## 1 · Architecture & Planning - [[SQL Server Architecture]] - [[SQL Server Query Processor]] - [[Query Optimizer]] - [[Execution Engine]] - [[Execution Plans]] - [[Execution Plan Properties]] - [[Query Store]] - [[Query Store Configuration and Usage]] - [[Database Engine Tuning Advisor]] - [[Data Structures]] --- ## 2 · Index Fundamentals & Types - [[Basic Index Terminology]] - [[Clustered Index]] - [[Non-Clustered Index]] - [[Clustered Index vs Heaps]] - [[Heap]] - [[Index Clustered Properties]] - [[Filtered Index]] - [[Covering Index]] - [[KEY vs INCLUDE]] - [[Missing Indexes]] - [[Unused Indexes]] --- ## 3 · Index Administration & Optimization - [[Index Creation And Administration]] - [[Index Fragmentation And Maintenance]] - [[Fragmentation and Index Maintenance]] - [[Index Operations]] - [[Index Optimization Guidelines]] - [[Index Usage and Optimization]] --- ## 4 · Data-Access Operators - [[Data Access Operators]] - [[Data Access Summary]] - [[Scan Operator]] - [[Seek Operator]] - [[Table Scan Operator]] - [[Index Scan Operator]] - [[Index Seek Operator]] - [[Bookmark Lookup Access Operation]] --- ## 5 · Join & Aggregate Operators - **Joins** - [[Nested Loops Join]] - [[Merge Join]] - [[Hash Join]] - [[Join Operators Performance]] - **Aggregates & Sorting** - [[Aggregation Operations]] - [[Stream Aggregate]] - [[Hash Aggregate]] - [[Sorting vs Hashing]] --- ## 6 · Statistics - [[Statistics]] - [[Exploring Statistics]] ---