Creating foreign tables is not really hard—however, it sometimes happens that people make mistakes, or maybe the passwords that have been used simply change. To handle such issues, PostgreSQL offers two commands: ALTER SERVER and ALTER USER MAPPING.

ALTER SERVER allows you to modify a server:

test=# h ALTER SERVER 
Command:  ALTER SERVER
Description: change the definition of a foreign server
Syntax:
ALTER SERVER name [ VERSION 'new_version' ]
      [ OPTIONS ( [ ADD | SET | DROP ] option ['value'] [, ... ] ) ] 
ALTER SERVER name OWNER TO { new_owner | CURRENT_USER | SESSION_USER } 
ALTER SERVER name RENAME TO new_name

We can use this command to add and remove options for a specific server, which is a good thing if we have forgotten something.

To modify user information, we can alter the user mapping as well:

test=# h ALTER USER MAPPING 
Command:   ALTER USER MAPPING
Description: change the definition of a user mapping
Syntax:
ALTER USER MAPPING FOR { user_name | USER | CURRENT_USER | SESSION_USER | PUBLIC }
   SERVER server_name
     OPTIONS ( [ ADD | SET | DROP ] option ['value'] [, ... ] )

The SQL/MED interface is regularly improved and, at the time of writing this book, features are being added. In the future, even more optimizations will make it to the core, making the SQL/MED interface a good choice for improving scalability.