On Sep 29, 2012, at 6:49, Matthias Nagel <matthias.h.na...@gmail.com> wrote:
> Hello, > > is there any way how one can store the result of a time-consuming calculation > if this result is needed more than once in an SQL update query? This solution > might be PostgreSQL specific and not standard SQL compliant. Here is an > example of what I want: > > UPDATE table1 SET > StartTime = 'time consuming calculation 1', > StopTime = 'time consuming calculation 2', > Duration = 'time consuming calculation 2' - 'time consuming calculation 1' > WHERE foo; > > It would be nice, if I could use the "new" start and stop time to calculate > the duration time. First of all it would make the SQL statement faster and > secondly much more cleaner and easily to understand. > > Best regards, Matthias > > You are allowed to use a FROM clause with UPDATE so if you can figure out how to write a SELECT query, including a CTE if needed, you can use that as your cache. An immutable function should also be optimized in theory though I've never tried it. David J. -- Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-sql
