Editing PostgreSQL (section)

=== Indexes ===
PostgreSQL includes built-in support for regular [[B-tree]] and [[hash table]] indexes, and four index access methods: generalized search trees ([[GiST]]), generalized [[inverted index]]es (GIN), Space-Partitioned GiST (SP-GiST)<ref name="SP-GiST" /> and [[Block Range Index]]es (BRIN). In addition, user-defined index methods can be created, although this is quite an involved process. Indexes in PostgreSQL also support the following features:

* [[Expression index]]es can be created with an index of the result of an expression or function, instead of simply the value of a column.
* [[Partial index]]es, which only index part of a table, can be created by adding a WHERE clause to the end of the CREATE INDEX statement. This allows a smaller index to be created.
* The planner is able to use multiple indexes together to satisfy complex queries, using temporary in-memory [[bitmap index]] operations (useful for [[data warehouse]] applications for joining a large [[fact table]] to smaller [[dimension table]]s such as those arranged in a [[star schema]]).
* [[k-nearest neighbors algorithm|''k''-nearest neighbors]] (''k''-NN) indexing (also referred to KNN-GiST<ref name="KNN-GiST" />) provides efficient searching of "closest values" to that specified, useful to finding similar words, or close objects or locations with [[Geographic data and information|geospatial]] data. This is achieved without exhaustive matching of values.
* Index-only scans often allow the system to fetch data from indexes without ever having to access the main table.
* [[Block Range Index]]es (BRIN).