pg_transform
   The catalog pg_transform stores information about
   transforms, which are a mechanism to adapt data types to procedural
   languages.  See CREATE TRANSFORM for more information.
  
Table 51.56. pg_transform Columns
| Name | Type | References | Description | 
|---|---|---|---|
| trftype | oid |  | OID of the data type this transform is for | 
| trflang | oid |  | OID of the language this transform is for | 
| trffromsql | regproc |  | The OID of the function to use when converting the data type for input to the procedural language (e.g., function parameters). Zero is stored if this operation is not supported. | 
| trftosql | regproc |  | The OID of the function to use when converting output from the procedural language (e.g., return values) to the data type. Zero is stored if this operation is not supported. |