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.
Separately, while testing various edge patterns I noticed that
`<-[]->` (full edge left or right) produces a syntax error:
SELECT count(*) FROM GRAPH_TABLE (g1 MATCH ()<-[]->() COLUMNS (1 AS one));
ERROR: syntax error at or near "->"
Per the standard BNF, this should be valid:
<full edge left or right> ::=
<left arrow bracket> <element pattern filler> <bracket right arrow>
i.e., `<-[]->` = `<-[` + `]->`. This is a separate parser issue,
not related to the implicit vertex insertion above.
Yes. That's a grammar issue. gram.y doesn't support it. Peter, do you
remember or know the reason why we don't support full edge left or
right? In fact, I am wondering what's the difference between full edge
left or right and full edge any direction?
<full edge left or right> is part of optional feature G043, which we
don't claim to support.
