Think Like the Cardinality Estimator

This session explains how SQL Server's cardinality estimator uses statistics to estimate row counts and how those estimates influence query plans. It examines multiple predicates, unknown parameter values, and values outside a histogram's range.

Syllabus

Introduction
Housekeeping
Session Evolution
How to contact me
About the session
Definitions
Pred selectivity
Example
Density
Density Example
cardiology estimation
SQL estimation
Execution plan
Why Cardinality Matters
Effects of Cardinality
Murphys Law
DBCC Statistics
Histogram
Explanation
Versions
Compatibility Level
Updated Stats
Actual Execution Plan
Multiple Predicates
What Changed
Parameter sniffing
Unknowns
Ascending Key