On 25.03.26 10:12, Ashutosh Bapat wrote:
On Wed, Mar 25, 2026 at 2:27 PM Peter Eisentraut <[email protected]> wrote:
On 23.03.26 16:00, Ashutosh Bapat wrote:
An empty pattern has no label expression which is equivalent to
disjunction of all applicable labels. If we add an empty pattern in
the rewrite phase, we will require its label expression to be resolved
in the rewrite phase. Looking at the proposed changes for all
properties reference [1], I am moving towards resolving the label
expression in the transformation stage itself. So I think it's better
to add the implicit vertex patterns during the transformation stage to
be future proof. Rewriter should just then rewrite the patterns into
joins and unions. Your point is correct that the implicit vertex
should not be visible in view definition or deparsed query. For that I
have added a flag implicit to GraphElementPattern.
GraphElementPatterns with implicit = true are ignored by ruleutils.
Implemented it that way in the attached patch.
Vertex patterns without an edge pattern in between are not supported
OTOH. Added an ereport for the same.
I have also added a few tests. I didn't add queries with all the
patterns you mentioned above. I tested a few by hand and all of them
worked as expected. Can you please check?
This functionality that you can leave off empty vertex patterns at the
beginning and end is part of the optional feature G047, which we don't
claim to support. So we should reject these path patterns.
Thanks for the clarification. What about the implicit empty vertex
patterns in the middle of the path? Should we reject these path
patterns also?
Yes, I think so.
The specification of feature G047 is:
"... in conforming SQL language, any <edge pattern> shall be immediately
preceded and followed by a <vertex pattern>."
So if you write
() -[]-> -[]-> ()
then the first edge pattern is not followed immediately by a vertex
pattern, and so it would be invalid without feature G047.
