http://msdn.microsoft.com/en-us/library/ms190806.aspx shows this lesser known performance trick. If a query uses a particular NCI (non-clustered-index), and all the output fields are “included” on the index, then query won't hit the data pages at all.
How about sybase? http://dba.stackexchange.com/questions/15319/equivalent-of-include-clause-while-creating-non-clustered-index-in-sybase says not supported. But See also https://support.ca.com/cadocs/0/CA%20ERwin%20Data%20Modeler%20r9%201-ENU/Bookshelf_Files/HTML/ERwin%20Help/index.htm?toc.htm?define_sybase_table_index_properties.html