Hi,
In order to implement some security features in our application, we
sometimes append additional WHERE filters to our queries, so the filer
in the end looks like:
SELECT ... FROM ... WHERE securityFilter1 AND securityFilter2 AND
securityFilter3
In the EXPLAIN the filters look something like:
(((SubPlan 1) = 'foo') AND ((SubPlan 2) = 'bar') AND ((SubPlan 3) = 'baz'))
There are no applicable indexes and each filter clause looks opaque to
the optimizer, so the optimizer is using some generic rules and assumes
that each AND clause would reduce the total number of returned rows by
some factor. The problem is that this is not usually the case, and
usually the clauses would not filter out any rows at all. This leads to
poor plans, when such query is a part of another bigger query.
Is there any trick to craft the query in such a way, so that to make the
optimizer believe that the filters would not remove any rows, and all
rows will likely be returned by the query?
Regards,
Vitaliy
