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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 33.13.
Table 43-22. 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 | int4 | pg_shadow.usesysid | Operator class owner |
| opcintype | oid | pg_type.oid | Input data type of the operator class |
| opcdefault | bool | True if this operator class is the default for opcintype | |
| opckeytype | oid | pg_type.oid | Type of index data, 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.