On 11/07/2011 20:19, David Salisbury wrote:
Hope someone's out there for this one. Basically I'm creating a summary
table of many
underlying tables in one select statement ( though that may have to
change ). My problem
can be shown in this example..
select my_function( timeofmeasurement, longitude ) as solarnoon,
extract(epoch from ( timeofmeasurement - solarnoon ) as solardiff
( case when solardiff < 3600 then 'Y' else 'N' end ) as within_solar_hour
from
my_table;
But I get an error along the lines of
ERROR: column "solarnoon" does not exist
LINE 8: extract(epoch from (timeofmeasurement - solarnoon) ) as sola...
One (slightly messy) way to do that is create another, outer layer of
SELECT - so your on-the-fly calculations are executed in the sub-select,
and the values are then available to the outer select. You have three
levels of dependency, so you'll need two subqueries:
<not tested>
select
x.solarnoon,
x.solardiff,
(case when x.solardiff < 3600 then 'Y' else 'N' end) as
within_solar_hour
from (
select
extract(epoch from (y.timeofmeasurement - y.solarnoon) as solardiff,
y.timeofmeasurement
from (
select
my_function(timeofmeasurement, longitude) as solarnoon,
timeofmeasurement
from
my_table
) y
) x;
</not tested>
I think you can also do it more elegantly with a CTE; not something I've
played with yet, but you can read about it here:
http://www.postgresql.org/docs/9.0/static/queries-with.html
HTH,
Ray.
--
Raymond O'Donnell :: Galway :: Ireland
rod@xxxxxx
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