Hello List,
I observed a strange behavior when I implemented a trigger function.
Given: Table "fcp_4258_kls_addr" with address points, Table
"fcp_4258_candidates" with some other points.
Objective: find closest point in fcp_4258_kls_addr to a point in
fcp_4258_candidates (from all found address points in a radius of 0.01 degrees
around the candidate).
After playing around with the statements I came up with this:
select s.id, ST_DistanceSphere(ST_SetSRID(ST_Point(6.951468, 50.93651),4258),
s.wkb_geometry) as klsdistancetocandidatem FROM kddb.fcp_4258_kls_addr s WHERE
ST_DWithin(s.wkb_geometry, ST_SetSRID(ST_Point(6.951468, 50.93651),4258), 0.01)
ORDER BY klsdistancetocandidatem ASC LIMIT 1;
I hope that the function does what I want: First select all addresses within
0.01 degrees distance to the point 6.951468, 50.93651 and then calculate the
distance to all of them. Order by distance in ascending order and select the
first which should be the closest to the questioned candidate.
This works fine when I run the statement manually in the console:
id | geo_kls_dist2candidate_m
----------+--------------------------
17553866 | 6.85436569
My goal was to save the closest address point (id) and the distance to the
table as soon as the candidate table is updated. The relevant line in the
trigger function for the trigger "BEFORE UPDATE ON candidates FOR EACH ROW
EXECUTE PROCEDURE" looks like this:
SELECT s.id, ST_DistanceSphere(s.wkb_geometry, NEW.wkb_geometry) INTO klsid,
klsdistancetocandidatem FROM kddb.fcp_4258_kls_addr s WHERE
ST_DWithin(s.wkb_geometry, NEW.wkb_geometry, 0.01) ORDER BY
klsdistancetocandidatem ASC LIMIT 1;
NEW.geo_kls_id = klsid;
NEW.geo_kls_distance2candidate_m = klsdistancetocandidatem;
I assumed that the trigger does the same as the select statement but I get a
different result for a candidate. The address point referenced in the
candidates table for the candidate with the coordinates 6.951468, 50.93651 is
497 meters away and not 6.8 meters.
Some findings:
* The id returned is within 0.01 degree radius for the candidate
* The address point with the given id has correctly referenced distance to
the candidate (but is not the closest)
* The address point returned does neither belong to the preceding candidate
point nor to the successive candidate (when sorted by primary key)
* The update trigger is fired and the procedure is executed (Tested with
various update statements)
The wkb_geometry doesn't change with the update. I have no idea why the address
points are different.
Can anybody help?
Michael
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