by Markus Winand.

Index Filter Predicates


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.

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Markus Winand teaches efficient SQL—inhouse and online. He minimizes the development time using modern SQL and optimizes the runtime with smart indexing—for that he also published the book SQL Performance Explained.

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