Postgres Plus Advanced Server Oracle Compatibility Developer's Guide :
ALTER USER -- change a database user account
ALTER USER name IDENTIFIED BY password
ALTER USER is used to change the password of a Postgres Plus Advanced Server user account. A database superuser or a user with the CREATEROLE privilege can use this command. Ordinary users can also use this command to change their own password.
The name of the user whose attributes are to be altered.
The new password to be used for this account.
Change a user password:
ALTER USER john IDENTIFIED BY xyz;