Andy Seaborne created JENA-881:
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Summary: Leaking from scope or dropping of filter expressions
Key: JENA-881
URL: https://issues.apache.org/jira/browse/JENA-881
Project: Apache Jena
Issue Type: Bug
Components: ARQ, Optimizer
Affects Versions: Jena 2.12.1, Jena 2.12.0, Jena 2.11.2
Reporter: Andy Seaborne
Assignee: Andy Seaborne
Fix For: Jena 2.13.0
This query (much reduced from a real example):
{noformat}
SELECT *
WHERE
{ { FILTER ( false ) }
UNION
{ FILTER ( ?z != 3 ) }
FILTER ( true )
}
{noformat}
generates this algebra before optimization (specifically, filter placement):
{noformat}
(filter true
(union
(filter false
(table unit))
(filter (!= ?z 3)
(table unit)))))
{noformat}
which is mis-optimized into:
{noformat}
(union
(filter (exprlist false true)
(table unit))
(filter true
(table unit)))
{noformat}
and gives a result of one row when it should be zero rows. This is because
the {{(!= ?z 3)}} has been lost.
Other cases leak the filter from its place in the tree:
{noformat}
(filter (!= ?x 4)
(extend ((?z 6))
(filter (= ?z 3)
(table unit))))
{noformat}
becomes:
{noformat}
(filter (exprlist (= ?z 3) (!= ?x 4))
(extend ((?z 6))
(table unit)))
{noformat}
which is wrong because the {{(= ?z 3)}} has moved outwards over the {{extend}}.
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