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 52.4. pg_amop Columns
| Name | Type | References | Description | 
|---|---|---|---|
| oid | oid | Row identifier (hidden attribute; must be explicitly selected) | |
| amopfamily | oid |  | The operator family this entry is for | 
| amoplefttype | oid |  | Left-hand input data type of operator | 
| amoprighttype | oid |  | Right-hand input data type of operator | 
| amopstrategy | int2 | Operator strategy number | |
| amoppurpose | char | Operator purpose, either sfor search orofor ordering | |
| amopopr | oid |  | OID of the operator | 
| amopmethod | oid |  | Index access method operator family is for | 
| amopsortfamily | oid |  | 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 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 B-tree operator family for the operator's result type.
  
    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'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.