Getting strange or unexpected results from SDO_GEOM.SDO_INTERSECTION?
Chances are that inverting the input geometries the result will be different.
This happens on Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.21.0.0.0.
I did find some cases where the intersection of A with B returns a simple polygon whereas B intersect A returns a geometry collection, that is a mix of point, lines and polygons.
Now, if I feed the result to function SDO_GEOM.SDO_BUFFER with a small negative radius, in one case I still get a valid polygon whilst in the other case I get a NULL.
As you can imagine this is somewhat disturbing as it may lead to a completely wrong result.
One workaround would be to always perform both operations and compare the results, albeit it's not clear whichever is the correct one in case they differ and it's not even clear if I should rely on the area of the resulting polygons for considering them "equal" or "equivalent".
In theory I'd say that the intersection of A with B should always match the intersection of B with A, however this is not what's happening so I am left wondering if this is a bug or an unpleasant side effect of the algorithm being used.
What I believe is really a bug instead is the behavior of SDO_GEOM.SDO_BUFFER when the input geometry is one of these geometry collections (SDO_GTYPE = 2004).
I'll submit these case to Oracle Support and see what they say, luckily I can supply a couple of test cases for them to look at.
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