PG_OPCLASS

PG_OPCLASS defines index access method operator classes.

Each operator class defines the semantics of index columns for a specific data type and a specific index access method. Essentially, an operator class specifies that a particular operator family is applicable to a specific indexable column data type. The set of operators in the family that are actually usable by the indexed column are those that accept the column's data type as their left-hand input.

**Table 1** PG_OPCLASS columns
Column	Type	Reference	Description
oid	oid	-	Row identifier (a hidden attribute that is only shown upon explicit selection).
opcmethod	oid	PG_AM.oid	Index access method the operator class belongs to.
opcname	name	-	Name of the operator class.
opcnamespace	oid	PG_NAMESPACE.oid	Namespace the operator class belongs to.
opcowner	oid	PG_AUTHID.oid	Owner of the operator class.
opcfamily	oid	PG_OPFAMILY.oid	Operator family containing this operator class.
opcintype	oid	PG_TYPE.oid	Data type of the operator class index.
opcdefault	Boolean	-	The value is true if the operator class is the default for opcintype.
opckeytype	oid	PG_TYPE.oid	Type of the index data. If it is the same as that of opcintype, the value is 0.

The opcmethod of an operator class must match the opfmethod of the operator family that contains it. Similarly, for any given combination of opcmethod and opcintype, there cannot be more than one PG_OPCLASS row with opcdefault set to true.

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