Speed Issue on an UPDATE from a sub-select

Question

Ignoring the fact this is a Spatial Query... having troubles understanding why a select finishes very quickly, yet putting the same select syntax in an UPDATE command as a sub-select takes forever to finish. Columns in the original table are indexed (ie SANITARY_MH_DATA.GIS_ID). The work-around has been to load a Temporary table with the sub-select results, followed by an UPDATE command. But it creates more sql code than needed.
Any hints appreciated.
Phil.
-- FIND THE SANITARY CATCHMENT THE MANHOLE IS IN --
-- need to add the ones that fall into more than 1 catchment
-- with the mask=TOUCH
UPDATE SANITARY_MH_DATA SET CATCHMENT_NAME = '';
-- THIS BLAZES AND IS DONE IN 5 SECONDS...
SELECT CATCHMENT_ID FROM
(SELECT A.GIS_ID AS MANHOLE, B.GIS_ID AS CATCHMENT_ID
FROM SANITARY_MH A, SANITARY_CATCHMENT B
WHERE SDO_RELATE (A.GEOMETRY,B.GEOMETRY, 'mask=INSIDE querytype=Window') = 'TRUE');
-- THIS BOGS DOWN AND TAKES FOREVER TO FINISH...
UPDATE SANITARY_MH_DATA SET CATCHMENT_NAME = ( SELECT CATCHMENT_ID FROM
(SELECT A.GIS_ID AS MANHOLE, B.GIS_ID AS CATCHMENT_ID
FROM SANITARY_MH A, SANITARY_CATCHMENT B
WHERE SDO_RELATE (A.GEOMETRY,B.GEOMETRY, 'mask=INSIDE querytype=Window') = 'TRUE')
WHERE SANITARY_MH_DATA.GIS_ID = A.MANHOLE);
EXIT;
Edited by: user13174287 on 24-Aug-2010 3:51 PM
Edited by: user13174287 on 24-Aug-2010 4:06 PM

Answer 1

There is such a way, however I doubt that it will work in your case. There are some restrictions on it.
You can write an update to a kind of inline query.
UPDATE (select dat.*, mh.GIS_ID AS MANHOLE, cat.GIS_ID CATCHMENT_ID
       from SANITARY_MH_DATA dat,  SANITARY_MH mh, SANITARY_CATCHMENT cat
       where SDO_RELATE (mh.GEOMETRY,cat.GEOMETRY, 'mask=INSIDE querytype=Window') = 'TRUE'
       and dat.GIS_ID = mh.GIS_ID
       ) v
SET v.CATCHMENT_NAME = v.CATCHMENT_ID
WHERE (v.CATCHMENT_NAME != v.CATCHMENT_ID or v.CATCHMENT_NAME is null)
;there is some join criteria missing between cat and dat. MAybe it would work if the CATACHMENT ID is fetched in the selct clause of the inline view, instead of joining it.
UPDATE (select dat.*, mh.GIS_ID AS MANHOLE,
                    (select cat.GIS_ID from SANITARY_CATCHMENT cat
                     where SDO_RELATE (mh.GEOMETRY,cat.GEOMETRY, 'mask=INSIDE querytype=Window') = 'TRUE'
                     and rownum = 1) as catchment_id
       from SANITARY_MH_DATA dat,  SANITARY_MH mh
       where dat.GIS_ID = mh.GIS_ID
       ) v
SET v.CATCHMENT_NAME = v.CATCHMENT_ID
WHERE (v.CATCHMENT_NAME != v.CATCHMENT_ID or v.CATCHMENT_NAME is null)
;Oh and there is the MERGE statement. This might help in your case.
Edited by: Sven W. on Aug 25, 2010 9:19 PM