From: Thomas Kellerer <spam_eater@gmx.net>
To: pgsql-sql@postgresql.org
Subject: Re: Reuse temporary calculation results in an SQL update query
Date: Sat, 29 Sep 2012 12:55:39 +0200
Message-ID: <k46k39$5th$1@ger.gmane.org> (raw)
In-Reply-To: <43516431.HfO3TYfNBy@hek506>
References: <43516431.HfO3TYfNBy@hek506>
Matthias Nagel wrote on 29.09.2012 12:49:
> 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.
Something like:
with my_calc as (
select pk,
time_consuming_calculation_1 as calc1,
time_consuming_calculation_2 as calc2
from foo
)
update foo
set startTime = my_calc.calc1,
stopTime = my_calc.calc2,
duration = my_calc.calc2 - calc1
where foo.pk = my_calc.pk;
http://www.postgresql.org/docs/current/static/queries-with.html#QUERIES-WITH-MODIFYING
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To: pgsql-sql@postgresql.org
Cc: spam_eater@gmx.net
Subject: Re: Reuse temporary calculation results in an SQL update query
In-Reply-To: <k46k39$5th$1@ger.gmane.org>
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