pg_opclass defines
index access method operator classes. Each operator class defines
semantics for index columns of a particular datatype and a particular
index access method. Note that there can be multiple operator classes
for a given datatype/access method combination, thus supporting multiple
behaviors.
Operator classes are described at length in the
Programmer's Guide.
Table 3-22. pg_opclass Columns
| Name | Type | References | Description |
|---|
| opcamid | oid | pg_am.oid | index access method opclass is for |
| opcname | name | | name of this opclass |
| opcnamespace | oid | pg_namespace.oid | namespace of this opclass |
| opcowner | int4 | pg_shadow.usesysid | opclass owner |
| opcintype | oid | pg_type.oid | type of input data for opclass |
| opcdefault | bool | | true if opclass is 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.
