Before version 11.70, database operations treated strings stored in all Informix databases as case-sensitive. For example, a query for the string "Central" returns "Central" but not "CENTRAL" or "central". Operations designed to disregard the case of text strings required a bts index or a functional index for each query.
In version 11.70, a database is still created as case-sensitive by default. However, you can use the NLSCASE INSENSITIVE option with the CREATE DATABASE statement to create a database that ignores the case of text strings. For example, querying "Central" returns "Central", "CENTRAL", and "central".
A case-insensitive database ignores letter case only on NCHAR and NVARCHAR data types, but it treats the other built-in character data types (CHAR, LVARCHAR, and VARCHAR) as case-sensitive. You cannot include both case-sensitive and case-insensitive databases in a distributed query.
For more information, see Specifying NLSCASE case sensitivity.