db-derby-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Uriah Eisenstein <uriaheisenst...@gmail.com>
Subject Are generated columns stored in the DB or calculated on the fly?
Date Thu, 02 Sep 2010 17:42:29 GMT
I searched around for the actual implementation of column "generated always
as <expression>" 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.

View raw message