Support for FETCH after PIPE

[jamieliu1023]

Discussed in #4188

^{Originally posted by chvr203 April 20, 2022}
Discussion around the nebula forums on with @wey-gu : https://discuss.nebula-graph.io/t/retrieve-all-edges-with-all-ranks-using-fetch-query/1195/5
I’m using a composite query involving GO and FETCH.
Query:
GO FROM “v1_id” over edgeName1 yield $$.v2.id as alliasId | FETCH PROP ON edgeName2 $-.alliasId → “v3_vid” YIELD properties(edge);
Example at: https://docs.nebula-graph.io/2.0/3.ngql-guide/7.general-query-statements/4.fetch/#use_fetch_in_composite_queries

Required Traversal: v1 → v2 → v3

I need to traverse from a known v1_vid to a known v3_vid. The output of v2_vid should be used as an input to the FETCH query (as the number of edges of type edgeName2 is around 2 Billion and FETCH performs faster).
With the above query, I get a syntax error at `’ YIELD '. Looks like the problem is while providing the v3_vid in the query, which can’t be harcoded/provided. But since the v3_vid needs to be provided by us, this query is not working.

Is there a workaround to provide the v3_vid by the user? Or is it mandatory for v3_vid to be an output of the GO query.

Feature Required: Add support for FETCH query after PIPE ( | ) so that the destination vertex can be a user defined string/ harcoded value.

[wey-gu]

#3984

[wey-gu]

we only support either both or non peer of the fetch prop edge pattern to be variable, that is.
we only support:

fetch on serve "player133" -> "team202"
yield "foo" as a, "bar" as bar | fetch on serve $-.a -> $-.b
while not support :

yield "foo" as a, "bar" as bar | fetch on serve $-.a -> "bar"