SDO_RELATE JOIN

Question

Oracle9i Question: Has anyone anywhere ever actually seen this spatial operator use the spatial index from both the tables in the join?
(Full table scans just won't cut it.)
Any hints, help, sample SQL or other insights are greatly appreciated.
Thank you.

Answer 1

In Oracle9i it is recommended that window queries be used when doing a spatial join. In Oracle Spatial 10g a new pseudo-operator sdo_join is introduced which will further enhance performance of spatial joins.
In Oracle9i, lets say you want to get all of the city/county pairs. Using the sample tables used for the course, there are 195 cities, and 3230 counties.
To get all of the city/county pairs, I would write the query as follows:
select /*+ ordered */ a.city, b.county
from geod_cities a, geod_counties b
where sdo_relate(b.geom, a.location,
'querytype=window mask=anyinteract') = 'TRUE';
Some notes on the query:
1) Use the ordered hint, and put the table the window comes from (geometry2) first in the from clause.
2) Use the table with smaller cardinality as the window table (note that cities has 195 rows, counties has 3230 rows).
3) If both tables have the same cardinality, and one has polygons and the other is of some other type, use the polygon table as the window table to enable the largest number of optimizations within spatial.
Hope this helps.