CODEWITHSUNDEEP
neo4jcypher
condit
condit

Reputation: 10962

Checking NULLS in an OPTIONAL MATCH

I have a cypher query like this:

MATCH (start:StartLabel)
OPTIONAL MATCH (start)-[:A]->(end1:EndLabel)
OPTIONAL MATCH (start)-[:B|C]->(middle:MiddleLabel)-[:D]->(end2:EndLabel)
WHERE NOT(end1 IS NULL AND end2 IS NULL)
RETURN *

In this graph model there are multiple valid ways to reach (end) from (start) but I want to make sure that the result matches at least one of the possible OPTIONAL MATCH paths. For some reason I continue to get results where both end1 and end2 are NULL with this WHERE clause. Am I missing something about how Cypher processes OPTIONAL MATCH and WHERE together?

Upvotes: 1

Views: 324

Answers (2)

cybersam
cybersam

Reputation: 67044

Here is an alternate way to get the results:

MATCH (start:StartLabel)-[:A]->(end:EndLabel)
RETURN start, NULL as middle, end
UNION
MATCH (start:StartLabel)-[:B|C]->(middle:MiddleLabel)-[:D]->(end:EndLabel)
RETURN start, middle, end

Upvotes: 2

Brian Underwood
Brian Underwood

Reputation: 10856

I've been told that WHERES always apply to the most previous (OPTIONAL )MATCH, so perhaps this will work?

MATCH (start:StartLabel)
OPTIONAL MATCH
  (start)-[:A]->(end1:EndLabel),
  (start)-[:B|C]->(middle:MiddleLabel)-[:D]->(end2:EndLabel)
WHERE NOT(end1 IS NULL AND end2 IS NULL)
RETURN *

As as aside, I feel like end1 IS NOT NULL OR end2 IS NOT NULL reads better to me

Upvotes: 0

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