Editing Ingres (database) (section)

===Indexes===
Ingres chooses ISAM (Index Sequential Access Method) as the index data structure by default, but also offers B+ Tree, Hash Table, and R-Tree as options. On Actian X, there is also two other options available only for X100 tables:<ref>{{cite web | url=https://docs.actian.com/actianx/11.2/index.html#page/SQLRef/CREATE_INDEX.htm | title=Actian X 11.2 Documentation }}</ref>
* '''X100_IX''': Default, creates a primary (clustered) index. Only one primary index per table is allowed.
* '''X100_SI''': Creates a secondary index on additional columns in an X100 table. Can also be specified as VWSI. Secondary indexes are not supported for partitioned tables.