How do I write this Neo4j Query?

Question

There are three node types: A, B and C.

I need all the A's and B's and only the C's that participate in exactly one relationship.

match (n)
where n:A or n:B or (n:C)-[]-()
with count(n) as countOfRels
where countOfRels > 0
return n

Not close, I know. I'm not sure where to go from here.

Answer 1

It's a bit strange that A, B and C do not seem to be related ... but here's how you could solve your question for C :

MATCH (n:C)
WHERE size((n)-[]-()) = 1
RETURN n
UNION
MATCH (n:A)
RETURN n
UNION
MATCH (n:B)
RETURN n;

Hope this helps.

Regards, Tom

Answer 2

you can use this

match(n)
where n:A OR n:B OR (n:C)-[r]-()
with count(r) as countOfRels
where countOfRels > 0
return n

Hope this helps.

Answer 3

You can do MATCH (a)--() WHERE NOT ()--(a)--() to match "nodes with only one relation". After that, You can use UNION or COLLECT()+UNWIND to combine the separate queries into one row result set.

// using Union
MATCH (n:C)--()
WHERE NOT ()--(n)--()
RETURN n
UNION
MATCH (n:A)
RETURN n
UNION
MATCH (n:B)
RETURN n;

// Using collect
OPTIONAL MATCH (a:A)
OPTIONAL MATCH (b:B)
OPTIONAL MATCH (c:C)--() WHERE NOT ()--(c)--()
WITH COLLECT(a)+COLLECT(b)+COLLECT(c) as nodez
UNWIND nodez as n
RETURN DISTINCT n