Please ignore the question below. It seems like Virtuoso is sensitive to
"redundant" (extra) semi-colons. I was using an extra semi-colon at the end
of Q2 unknowingly, and so it was repeatedly giving a syntax error.
Without an extra semi-colon, Q2 now runs as expected without syntax error.
On Thu, Mar 5, 2015 at 2:05 PM, Medha Atre <medha.a...@gmail.com> wrote:
> Hi,
>
> I am trying to run some SPARQL queries translated to SQL on NATIVE
> Virtuoso columnstore, which involve combination of left join and UNION
> statements.
>
> A sample SPARQL query is given below:
>
> *Q1:*
>
> SPARQL SELECT * FROM <http://mytest.com>
> WHERE {
> ?a <http://ex.com/11> <http://ex.com/1> .
> OPTIONAL {
> {?a <http://ex.com/11> <http://ex.com/1> .
> OPTIONAL {?a <http://ex.com/12> ?b .}
> }
> UNION
> {?a <http://ex.com/11> <http://ex.com/1> .
> OPTIONAL {?b <http://ex.com/11> ?a .}
> }
> }
> }
>
> Now, to run this as an SQL query, I stored the same data from the graph <
> http://mytest.com> in a 3-column table called "mytest", and translated
> the above query to SQL as below:
>
>
>
> *Q2:*SELECT * FROM
> (select s as a from mytest where p=11 and o=1) as t1
> left join
> (select t2.s as a, t3.o as b from
> (select s from mytest where p=11 and o=1) as t2
> left join
> (select s, o from mytest where p=12) as t3
> on t2.s=t3.s
> UNION ALL
> select t4.s as a, t5.s as b from
> (select s from mytest where p=11 and o=1) as t4
> left join
> (select s, o from mytest where p=11) as t5
> on t4.s=t5.o) t7
> on t1.a=t7.a;
>
> *The problem is* -- while Q1 runs fine on Virtuoso, Q2 keeps giving me
> syntax a error at the very last line (on t1.a=t7.a). I checked Virtuoso's
> SQL grammar at http://docs.openlinksw.com/virtuoso/SELECTSTMT.html as
> well as looked at the abstract representation of Q1 through "set explain
> on". But neither of this has helped me to know where I am going wrong.
>
> Any other SQL query with only left joins, without UNION statement run
> correctly, but as soon as do a left join over a UNION ALL statement, it
> gives a syntax error. To debug more, I tried running just the subquery of
> Q2 having only UNION ALL as
>
> *Q3:*
> select t2.s as a, t3.o as b from
> (select s from mytest where p=11 and o=1) as t2
> left join
> (select s, o from mytest where p=12) as t3
> on t2.s=t3.s
> UNION ALL
> select t4.s as a, t5.s as b from
> (select s from mytest where p=11 and o=1) as t4
> left join
> (select s, o from mytest where p=11) as t5
> on t4.s=t5.o) t7
>
> *Q3 runs correctly, but Q2 refuses to run by giving syntax error.*
>
> Can the Virtuoso support staff or the users let me know how to correctly
> write Q2 to make it run on the native SQL engine? *Please note* that I
> have to run the SQL format of the query to do some native SPARQL vs SQL
> experiments, so solutions like "just run the SPARQL query only" will not be
> useful!
>
> Thanks in anticipation.
>
> Medha
>
>
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