Details
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Type:
Sub-task
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Status: Done
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Priority:
Medium
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Resolution: Done
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Affects Version/s: None
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Fix Version/s: BLAZEGRAPH_RELEASE_1_5_2
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Component/s: None
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Labels:None
Description
With a database containing the quad in the data.nq file the following query:
SELECT ?uri_d WHERE {
VALUES ?type
GRAPH <http://graph1>
{ ?uri_d <http://p> ?type . }}
return the expected result:
| uri_d |
|---|
| <http://subj> |
wrapping this query in another which projects the inner variable:
select ?uri_d where {
SELECT ?uri_d WHERE {
VALUES ?type
GRAPH <http://graph1>
{ ?uri_d <http://p> ?type . }}
}
returns no matches. Changing the outer projection to * also returns no results.
However, projecting the unused variable ?type from the inner query does cause the result to be returned again:
SELECT ?uri_d WHERE {
SELECT ?type ?uri_d WHERE {
VALUES ?type
GRAPH <http://graph1>
{ ?uri_d <http://p> ?type . }}
}
returns
| uri_d |
|---|
| <http://subj> |
again as expected.
Fixed in branch bindings-refactor, added ticket as a test case. Just re-running govtrack to get hints on performance regressions, once this succeeds the branch will be merged into master.
The fix was part of a major refactoring. The prior optimizers ASTSimpleBindingsOptimizer, ASTValuesOptimizer, and ASTBindingsAssigner were retired, and custom code for extracting static bindings (outside of optimizers) was eliminated. All cases were generalized in the ASTStaticBindingsOptimizer, which analyzes the query to detect statically derivable bindings introduced via constructs (such as BIND/VALUES, FILTER with sameTerm, IN or term equality over URIs). These bindings are pulled out to the top-level clause where valid (according to the bottom up semantics) and inlines them at various positions. The refactoring is backed by a broad set of test cases, including both SPARQL level and AST level tests.