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 51.55. pg_transform Columns
| Column Type Description | 
|---|
| 
        Row identifier | 
| 
        OID of the data type this transform is for | 
| 
        OID of the language this transform is for | 
| 
        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. | 
| 
        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. |