43.24. `pg_opclass`

The catalog pg_opclass defines index access method operator classes. Each operator class defines semantics for index columns of a particular data type and a particular index access method. Note that there can be multiple operator classes for a given data type/access method combination, thus supporting multiple behaviors.

Operator classes are described at length in Section 33.14.

Table 43-24. pg_opclass Columns

Name	Type	References	Description
`opcamid`	`oid`	`pg_am.oid`	Index access method operator class is for
`opcname`	`name`		Name of this operator class
`opcnamespace`	`oid`	`pg_namespace.oid`	Namespace of this operator class
`opcowner`	`oid`	`pg_authid.oid`	Owner of the operator class
`opcintype`	`oid`	`pg_type.oid`	Data type that the operator class indexes
`opcdefault`	`bool`		True if this operator class is the default for `opcintype`
`opckeytype`	`oid`	`pg_type.oid`	Type of data stored in index, or zero if same as `opcintype`

The majority of the information defining an operator class is actually not in its pg_opclass row, but in the associated rows in pg_amop and pg_amproc. Those rows are considered to be part of the operator class definition — this is not unlike the way that a relation is defined by a single pg_class row plus associated rows in pg_attribute and other tables.