The pg_opclass system catalog table 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. An operator class essentially specifies that a particular operator family is applicable to a particular indexable column data type. The set of operators from the family that are actually usable with the indexed column are those that accept the column’s data type as their left-hand input.

    An operator class’s opcmethod must match the opfmethod of its containing operator family. Also, there must be no more than one pg_opclass row having opcdefault true for any given combination of opcmethod and opcintype.

    column type references description
    oid oid Row identifier (hidden attribute; must be explicitly selected)
    opcmethod 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
    opcfamily oid pg_opfamily.oid Operator family containing the operator class
    opcintype oid pg_type.oid Data type that the operator class indexes
    opcdefault boolean True if this operator class is the default for the data type opcintype
    opckeytype oid pg_type.oid Type of data stored in index, or zero if same as opcintype

    Parent topic: System Catalogs Definitions