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47.4. pg_amop

The catalog pg_amop stores information about operators associated with access method operator families. There is one row for each operator that is a member of an operator family. A family member can be either a search operator or an ordering operator. An operator can appear in more than one family, but cannot appear in more than one search position nor more than one ordering position within a family. (It is allowed, though unlikely, for an operator to be used for both search and ordering purposes.)

Table 47-4. pg_amop Columns

Name Type References Description
oid oid   Row identifier (hidden attribute; must be explicitly selected)
amopfamily oid pg_opfamily.oid The operator family this entry is for
amoplefttype oid pg_type.oid Left-hand input data type of operator
amoprighttype oid pg_type.oid Right-hand input data type of operator
amopstrategy int2   Operator strategy number
amoppurpose char   Operator purpose, either s for search or o for ordering
amopopr oid pg_operator.oid OID of the operator
amopmethod oid pg_am.oid Index access method operator family is for
amopsortfamily oid pg_opfamily.oid The btree operator family this entry sorts according to, if an ordering operator; zero if a search operator

A "search" operator entry indicates that an index of this operator family can be searched to find all rows satisfying WHERE indexed_column operator constant. Obviously, such an operator must return boolean, and its left-hand input type must match the index's column data type.

An "ordering" operator entry indicates that an index of this operator family can be scanned to return rows in the order represented by ORDER BY indexed_column operator constant. Such an operator could return any sortable data type, though again its left-hand input type must match the index's column data type. The exact semantics of the ORDER BY are specified by the amopsortfamily column, which must reference a btree operator family for the operator's result type.

Note: At present, it's assumed that the sort order for an ordering operator is the default for the referenced opfamily, i.e., ASC NULLS LAST. This might someday be relaxed by adding additional columns to specify sort options explicitly.

An entry's amopmethod must match the opfmethod of its containing operator family (including amopmethod here is an intentional denormalization of the catalog structure for performance reasons). Also, amoplefttype and amoprighttype must match the oprleft and oprright fields of the referenced pg_operator entry.

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