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42.24. 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 32.14.

Table 42-24. 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.

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