# Working with cardinality statistics

Cardinality Statistics are gathered on the keys of an index when the index is created.

- When cardinality statistics are automatically updated
- When cardinality statistics go stale

Parent topic: Selectivity and cardinality statistics
Related concepts
Determinations of rows scanned from disk for a table scan
Estimations of rows scanned from disk for an index scan
Statistics-based versus hard-wired selectivity
What are cardinality statistics?