There are two different ways databases use indexes to apply the where clauses (predicates):
As access predicates
The access predicates express the start and stop conditions for the leaf node traversal.
As filter predicates
Filter predicates are applied during the leaf node traversal only. They don’t contribute to the start and stop conditions and do not narrow the scanned range.
Important
Access and filter predicates are attributes of explain plan operations—not index attributes.
That means that different where clauses can use different access and filter predicates on the same index.
Links
The impact of accidental index filter predicates demonstrated
Spotting index filter predicates in Oracle, PostgreSQL and SQL Server execution plans.
