There is a new interesting article about creating case insensitive databases with Informix. This new functionality is available in Informix 11.70.xC2.

The article desribes why this new feature is more sophisticated than creating a functional index on a column or selecting data with the lower() or upper() function. Case-Insensitivity with Informix 11.70.xC2 applies to constraints, fragmentation schemes, group by/unique/distinct functions, order by and other SQL operations.