Case insensitive columns

I have a problem similar to that described by Shaw Terwilliger on
2001-03-14 (Subject: Case Insensitive CHECK CONSTRAINTs):

I need some case insensitive char/varchar columns. A unique index on
lower(col_name) would help to avoid multiple entries only differing in
case. But it would be nice if existing applications which rely on case
insensitivity need not be changed. Also, I get foreign key constraint
violations when importing case insensitive data from Sybase.

How can I define case insensitive variants of all character types? Or
are there any other solutions?

Thanks!

--
Christoph Strebin

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