Hi Peter -
(This comment has nothing to do with your original question; however,
the query caught my eye):
You query is probably not as efficient as it can be. If you read the
documentation for PostGIS about "ST_Expand":
-- quote --
Pre version 1.3, ST_Expand was used in conjunction withST_Distance
<https://postgis.net/docs/ST_Distance.html>to do indexable distance
queries. For example,|geom && ST_Expand('POINT(10 20)', 10) AND
ST_Distance(geom, 'POINT(10 20)') < 10|. This has been replaced by the
simpler and more efficientST_DWithin
<https://postgis.net/docs/ST_DWithin.html>function.
-- quote end --
So if you're using a PostGIS later than 1.3 you could improve the query
by doing this:
drop table if exists stevns_test_urban_ped; create table
stevns_test_urban_ped as select urban.id as id, urban.geom as geom,
min(urban.pop2019) as pop2019, count(forest) as ped,
min(urban.pop2019)/(count(forest)+1)::float as pop_forest_ped from
(select * from stevns_test_p where lu_type = 1) as urban join (select *
from stevns_test_p where lu_type = 2) as forest on
*ST_DWithin(urban.geom, forest.geom, 1000.0)* group by urban.id*,
urban.geom* ;
Med venlig hilsen / Best regards
Bo Victor Thomsen
Den 17-10-2022 kl. 09:04 skrev Hans Skov-Petersen via Qgis-user:
Dear Michael
Functional dependencies are, according the Net, applied in
PostgreSQL:https://stackoverflow.com/questions/66065987/postgres-sql-column-must-appear-in-the-group-by-clause-or-be-used-in-an-aggrega
And accordingly, you shouldn't worry about it in PostGIS. The funny thing is
that sometime it works. Sometimes it doesn't.
Cheers
Hans
-----Original Message-----
From: Qgis-user<[email protected]> On Behalf Of Reetz, Michael
(NLPV) via Qgis-user
Sent: 17. oktober 2022 08:47
To:[email protected]
Subject: Re: [Qgis-user] Functional dependency seem not working in group
Hello Hans,
as far as I know, it is an SQL rule, that all selected attributes that are not
queried with an aggregate function have to be part of the group by clause. If
you run that query, your database server will check the syntax and throw that
error. I'm not sure if the SQL server realizes the 'functional dependency' in
your query as assumed by you.
Cheers,
Michael
-----Ursprüngliche Nachricht-----
Von: Qgis-user<[email protected]> Im Auftrag von Hans
Skov-Petersen via Qgis-user
Gesendet: Montag, 17. Oktober 2022 08:00
An:[email protected]
Betreff: [Qgis-user] Functional dependency seem not working in group
Dear Friends
I have, what appears to be a classic problem: When running a selection including a group
statement I get the good old 'ERROR: column "urban.geom" must appear in the
GROUP BY clause or be used in an aggregate function'.
I thought 'functional dependency' was in place to take care of that. The way I
understand it, is that functional dependency will, as applied in e.g. the group
statement, realize that e.g. the geom field is uniquely related to the id field
(which is referred in the group statement). Am I right in my assumption?
This is the ode causing the trouble:
drop table if exists stevns_test_urban_ped; create table stevns_test_urban_ped
as
select urban.id as id, urban.geom as geom, min(urban.pop2019) as pop2019,
count(forest) as ped, min(urban.pop2019)/(count(forest)+1)::float as
pop_forest_ped
from (select * from stevns_test_p where lu_type = 1) as urban
join (select * from stevns_test_p where lu_type = 2) as forest on
ST_Distance(urban.geom, forest.geom) < 1000 and forest.geom &&
(ST_Expand(urban.geom, 1000))
group by urban.id
;
Never mind the logics or meaning :-)
Thanks
Cheers
Hans
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