# When cardinality statistics are automatically updated

For the following operations that you perform on a table, Derby automatically creates new statistics or updates existing statistics:

- When you create a new index on an existing non-empty table. Statistics are automatically created for only the new index.
- When you add a primary key, unique, or foreign key constraint to an existing non-empty table. If there is no existing index that can be used for the new key or constraint, Derby automatically creates statistics for only the new indexes.
- When you run the SYSCS_UTIL.SYSCS_COMPRESS_TABLE system procedure. Statistics are created automatically for all indexes if the statistics do not already exist.
- When you drop a column that is part of a table's index, the statistics for the affected index are dropped. Statistics are automatically updated for the other indexes on the table.

Parent topic: Working with cardinality statistics
Related concepts
When cardinality statistics go stale