MSDN Documentation

Query Processing Overview

SQL Server's query processing engine transforms T‑SQL statements into efficient execution strategies. It consists of parsing, algebrizing, optimization, and execution phases.

  • Parsing and Binding
  • Algebraic Transformation
  • Cost‑Based Optimization
  • Plan Generation
  • Execution and Runtime

Query Optimizer

The cost‑based optimizer evaluates multiple logical and physical alternatives to produce the lowest‑cost execution plan.

SELECT TOP 10 *
FROM Sales.OrderDetails
WHERE UnitPrice > 100
ORDER BY OrderDate DESC;

Key optimizer features include:

  • Rule‑based and cost‑based optimization
  • Statistics‑driven decisions
  • Parallelism and query hints

Execution Plans

Execution plans visualize how SQL Server will access data. Use SET SHOWPLAN_XML ON or the graphical plan in SSMS.

Sample Execution Plan

Tools & Utilities

Several tools help you analyze and tune query performance.

  • SQL Server Management Studio (SSMS)
  • Database Engine Tuning Advisor (DTA)
  • Query Store
  • Dynamic Management Views (DMVs)

Best Practices

  1. Keep statistics up to date.
  2. Avoid SELECT *
  3. Use appropriate indexes.
  4. Prefer set‑based operations over cursors.
  5. Leverage query hints sparingly.

Further Reading