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. 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 whichever ones accept the column's data type
as their left-hand input.
Operator classes are described at length in Section 37.14.
Table 51.33. pg_opclass Columns
| Name | Type | References | Description |
|---|---|---|---|
oid | oid | Row identifier (hidden attribute; must be explicitly selected) | |
opcmethod | oid | | Index access method operator class is for |
opcname | name | Name of this operator class | |
opcnamespace | oid | | Namespace of this operator class |
opcowner | oid | | Owner of the operator class |
opcfamily | oid | | Operator family containing the operator class |
opcintype | oid | | Data type that the operator class indexes |
opcdefault | bool | True if this operator class is the default for opcintype | |
opckeytype | oid | | Type of data stored in index, or zero if same as opcintype |
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.