Unless you intend to make use of Oracle provided features that are not
available with Informix there are for all practical purposes no
advantages of Oracle over Informix.
Having said that Oracle is a very good all around rdbms that works well
with small to large concurrent user loads with small to very large
physical databases in OLTP, DSS, or Warehouse environments. Oracle
supports most all of the ANSI 92 syntax. It comes complete with a wide
range of single row functions including the ANSI trim, nullif, and
coalesce. Date format manipulation and date math in Oracle is very
nice and fairly simple: to_date, to_char, add_months, last_day.
Oracle 10g includes the ability to recover dropped objects, show a
history of changes to a row, and flash a table back to a point in time
for querying. Many routine maintenance tasks can be performed while
the data is still available for update activity.
HTH -- Mark D Powell --