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https://issues.apache.org/jira/browse/JENA-97?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13123520#comment-13123520
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Andy Seaborne commented on JENA-97:
-----------------------------------
Simon -
I presume you actually mean the same variable appears in the iterator of
variables more than once. The bindings themselves (rows) have no duplicates.
The variable should not be repeated but it is always bound to the same
value.The var/value is cached in the immediate TDB level, with it's NodeId, by
copy-down from the parent. Only one is accessed by "get" and the variable
should only appear once in teh list of variable names.
In the results table above, there are no duplicates (some spellings are very
similar). Execution proceeds by finding 3 choices for ?aUri. These pass to the
path. There are 3 possibilties for ?aUri = <eomer.nt>, 2 for <eomer.nt> and 1
for <theodred.nt>. TDB agrees with an in-memory execution.
TDB 0.8.7 didn't always correctly execute paths outside the storage default
graph so the query, for other reasons, returned no rows.
> TDB 0.9.0 snapshot sometimes returns a SELECT binding twice
> -----------------------------------------------------------
>
> Key: JENA-97
> URL: https://issues.apache.org/jira/browse/JENA-97
> Project: Jena
> Issue Type: Bug
> Components: TDB
> Environment: tx-tdb-0.9.0-20111006.082548-13-dist
> Reporter: Simon Helsen
> Assignee: Andy Seaborne
> Attachments: quads.txt
>
>
> Very sometimes (rare), it seems that a result set will repeat the first
> SELECT binding. E.g.
> SELECT ?a ?b ...
> will bind ?a twice in the result set. It only happens quite rarely, but the
> same queries behave correctly in TDB 0.8.7.
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