pg_cast stores data type conversion paths, both built-in paths and those defined with CREATE CAST.
Table 3-8. pg_cast Columns
| Name | Type | References | Description |
|---|---|---|---|
| castsource | oid | pg_type.oid | OID of the source data type |
| casttarget | oid | pg_type.oid | OID of the target data type |
| castfunc | oid | pg_proc.oid | The OID of the function to use to perform this cast. Zero is stored if the data types are binary coercible (that is, no run-time operation is needed to perform the cast). |
| castcontext | char | Indicates what contexts the cast may be invoked in. e means only as an explicit cast (using CAST, ::, or function-call syntax). a means implicitly in assignment to a target column, as well as explicitly. i means implicitly in expressions, as well as the other cases. |