Hidden column significance in table? [duplicate]

开发者_开发问答This question already has answers here: Closed 12 years ago.

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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.

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