Microsoft:
(edited: man what a day)
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/odbc/htm/odbcsqlstatistics.asp
(bottom of the page, thanks to Paul Rogers, I'm not sure I ever would have found it on my own.)
For Oracle, you probably want to avoid the indexes() function, and do queries straight to the system tables:
http://www.ss64.com/orad/ALL_IND_COLUMNS.html
http://www.ss64.com/orad/DBA_INDEXES.html
(edited: man what a day)
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/odbc/htm/odbcsqlstatistics.asp
(bottom of the page, thanks to Paul Rogers, I'm not sure I ever would have found it on my own.)
For Oracle, you probably want to avoid the indexes() function, and do queries straight to the system tables:
http://www.ss64.com/orad/ALL_IND_COLUMNS.html
http://www.ss64.com/orad/DBA_INDEXES.html