Tpt commented on issue #1615:
URL: https://github.com/apache/jena/issues/1615#issuecomment-1312734166
> The current design is to have a operator in the algebra lateral. I'll PR a
working branch (it's in my development clone ATM).
> While it is related to sequence of one or two elements, my preference is
to have a separate operator which can have it's own definition. sequence is
specific to the ARQ optimizer and implies certain conditions on its arguments.
Thank you! It definitely make sense.
>> LATERAL is modifying pattern evaluation, opposite to e.g. OPTIONAL, UNION
or MINUS
> An existing example that is not so different is FILTER ( NOT EXISTS { ...
} ).
That's a good point! Indeed, we have to already introduced the substitution
operator for FILTER NOT EXISTS so having it inside of the "lateral" operator
definition make sense. This gives a good definition of `LATERAL {` and, so, it
make sense to have it as a "standalone" operator and not as a modifier of
"optional", "graph"... This is the piece I was missing. I am now convinced by
your proposal and it looks like the best design I have seen at the moment.
> Digression: It would be nice to have "SELECT-less" (sub)queries: { ?s ?p
?o } LIMIT 1
Yes, to avoid the `SELECT *` but it's minor syntactic sugar imho.
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