52.4. pg_amop
The catalogpg_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 asearch operator or anordering 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 52.4. pg_amop Columns
Column Type Description |
|---|
Row identifier |
The operator family this entry is for |
Left-hand input data type of operator |
Right-hand input data type of operator |
Operator strategy number |
Operator purpose, either |
OID of the operator |
Index access method operator family is for |
The B-tree 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 satisfyingWHEREindexed_columnoperatorconstant. Obviously, such an operator must returnboolean, 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 byORDER BYindexed_columnoperatorconstant. 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 theORDER BY are specified by theamopsortfamily column, which must reference a B-tree 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 operator family, i.e.,ASC NULLS LAST. This might someday be relaxed by adding additional columns to specify sort options explicitly.
An entry'samopmethod must match theopfmethod of its containing operator family (includingamopmethod here is an intentional denormalization of the catalog structure for performance reasons). Also,amoplefttype andamoprighttype must match theoprleft andoprright fields of the referencedpg_operator entry.