Hidden column significance in table?

Question

Possible Duplicates:
metadata for determining unsed columns
How can you tell which columns are unused in ALL_TAB_COLS?

Hi, I have to fetch only used column names from all_tab_cols only not unsused ,may i know hidden_column column is marked 'Y' for unused_column only or their some other reasons also.

Answer 1

In 11g, function-based indexes are implemented as a virtual column (i.e. (column1 + column2)) and are marked as a hidden column.