ALTER USER MAPPING
Name
ALTER USER MAPPING -- change the definition of a user mapping
Synopsis
ALTER USER MAPPING FOR { user_name | USER | CURRENT_USER | PUBLIC }
    SERVER server_name
    OPTIONS ( [ ADD | SET | DROP ] option ['value'] [, ... ] )Description
Note: The following description applies only to Postgres-XC
   USER MAPPING has not been supported
   by Postgres-XC yet.  This command may be supported
   in the future releases.