* non-unique index on the first parts of a longish text field (SUBSTRING(field)) to save disk space, while still allowing faster searches than a sequential scan.
* indexing on LOWER(field)/UPPER(field) to allow case-insensitive searches or case-insensitive unique constraint.
In what other scenario are you using functional index? Searching the archives, I found someone indexing a date as 'YYYYMMDD', probably to allow searching using LIKE 'YYYY%' or LIKE 'YYYYMM%'. I've also thought creating a REVERSE_DOT(field) function for IP addresses and hostnames to allow wildcard searches (*.yahoo.com) using 'REVERSE_DOT(f) LIKE 'com.yahoo.%'. Has anyone done something like this?
-- dave
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