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From Knut Anders Hatlen <knut.hat...@ORACLE.COM>
Subject Re: Are generated columns stored in the DB or calculated on the fly?
Date Thu, 02 Sep 2010 20:46:16 GMT
Uriah Eisenstein <uriaheisenstein@gmail.com> writes:

> Hi,
> I searched around for the actual implementation of column "generated
> always as " but couldn't find anything, except maybe by
> digging into Derby source code which I don't want to... I want to
> know whether a generated column is a "real" column existing within
> the DB storage, and is updated whenever the columns it depends on are
> updated - or is it a "virtual" column which is recalculated whenever
> it is read. I don't have a specific need for it right now, but such
> columns can be useful for indexing and such, e.g. of case-insensitive
> strings or of UDTs, so I think it is useful to know whether the price
> is mainly in space requirements (if they're "real") or just in
> performance when reading.

Hi Uriah,

The generated columns are physical columns stored in the tables, and
they are updated whenever a column they reference changes. You can also
create indexes on the generated columns.

Knut Anders

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