52.33. pg_opclass
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## 52.33. 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 36.16.

Table 52.33. pg_opclass Columns

Column Type Description
`oid` oid Row identifier
`opcmethod` oid (references pg_am.`oid`) Index access method operator class is for
`opcname` name Name of this operator class
`opcnamespace` oid (references pg_namespace.`oid`) Namespace of this operator class
`opcowner` oid (references pg_authid.`oid`) Owner of the operator class
`opcfamily` oid (references pg_opfamily.`oid`) Operator family containing the operator class
`opcintype` oid (references pg_type.`oid`) Data type that the operator class indexes
`opcdefault` bool True if this operator class is the default for `opcintype`
`opckeytype` oid (references pg_type.`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`.

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