pg_cast stores data type conversion paths, both built-in paths and those defined with CREATE CAST.
Table 3-8. pg_cast Columns
|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.|