Mhh. I have no clue about the internals of PostgreSQL and query planing, but to me as user this should really be a thing the optimizer has to work out..

On 03.04.2005 10:01, PFC wrote:

Noticed this problem,too.
You can always make the calculation you want done once inside a set returning function so it'll behave like a table, but that's ugly.

On Mon, 28 Mar 2005 16:14:44 +0200, Hannes Dorbath <[EMAIL PROTECTED]> wrote:

hm, a few days and not a single reply :|

any more information needed? test data? simplified test case? anything?


Hannes Dorbath wrote:

The query and the corresponding EXPLAIN is at
I'd like to use the column q.replaced_serials for multiple calculations
in the SELECT clause, but every time it is referenced there in some way
the whole query in the FROM clause returning q is executed again.
This doesn't make sense to me at all and eats performance.
If this wasn't clear enough, for every
q.replaced_serials <insert_random_calculation> AS some_column
in the SELECT clause there is new block of
-> Aggregate (cost=884.23..884.23 rows=1 width=0)
-> Nested Loop (cost=0.00..884.23 rows=1 width=0)
-> Index Scan using ix_rma_ticket_serials_replace on
rma_ticket_serials rts (cost=0.00..122.35
rows=190 width=4)
Index Cond: ("replace" = false)
-> Index Scan using pk_serials on serials s
(cost=0.00..3.51 rows=1 width=4)
Index Cond: (s.serial_id = "outer".serial_id)
Filter: ((article_no = $0) AND (delivery_id = $1))
in the EXPLAIN result.
For those who wonder why I do this FROM (SELECT...). I was searching for
a way to use the result of an subselect for multiple calculations in the
SELECT clause and return that calculation results as individual columns.
I tested a bit further and found out that PG behaves the same in case q
is a view. This makes me wonder how efficient the optimizer can work
with views - or even worse - nested views.
Tested and reproduced on PG 7.4.1 linux and 8.0.0 win32.
Thanks in advance,
Hannes Dorbath

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