Home

	Expand Search

Performance and Tuning Guide

Chapter 5: Understanding the Query Optimizer

Chapter 5

This chapter introduces the Adaptive Server query optimizer and explains the steps performed when you run queries. It explains how statistics are used to analyze search arguments and join clauses.

This chapter contains the following sections:

• What Is Query Optimization?
• Adaptive Server's Cost-Based Optimizer
• Factors Examined During Query Optimization
• How Preprocessing Adds Optimizable Clauses
• Search Arguments and Useful Indexes
• Join Syntax and Join Processing
• Datatype Mismatches and Query Optimization
• Guidelines for Creating Search Arguments
• Splitting Stored Procedures to Improve Costing

This chapter explains how costs for individual query clauses are determined. Chapter 6, "Access Methods and Query Costing for Single Tables," explains how these costs are used to estimate the logical, physical, and total I/O cost for single table queries.

Chapter 7, "Access Methods and Query Costing for Joins and Subqueries," explains how costs are used when queries join two or more tables, or when queries include subqueries.

What Is Query Optimization?

Adaptive Server's Cost-Based Optimizer

Factors Examined During Query Optimization

How Preprocessing Adds Optimizable Clauses

Search Arguments and Useful Indexes

Guidelines for Creating Search Arguments

Join Syntax and Join Processing

Datatype Mismatches and Query Optimization

Splitting Stored Procedures to Improve Costing