hm, a few days and not a single reply :|
any more information needed? test data? simplified test case? anything?
thanks
Hannes Dorbath wrote:
The query and the corresponding EXPLAIN is at
http://hannes.imos.net/query.txt
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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