Neo4j / Cypher：计算与模式匹配的不同节点组合

Question

I query paths within a Neo4j graph. The path contains more than two nodes. I want to count the distinct occurences of a two-node subpath.

So in the following example I want to know the number of the resulting rows:

MATCH ()-->(n1:Label1)-->(n2:Label2)-->()
RETURN DISTINCT n1, n2

Eg something like

RETURN count(DISTINCT n1, n2)

(which would work for a single node: RETURN count(DISTINCT n1) )

How can I do this in Cypher?

Answer 1

Do this to get the number of times each distinct n1 and n2 combination is found:

MATCH ()-->(n1:Label1)-->(n2:Label2)-->()
RETURN n1, n2, COUNT(*);

Aggregating functions like COUNT use non-aggregating items in the same WITH or RETURN clause as unique "grouping keys" (so no need to use DISTINCT ).

[UPDATE]

To get the number of distinct n1 and n2 combinations, you can aggregate twice in this somewhat hacky query:

MATCH ()-->(n1:Label1)-->(n2:Label2)-->()
WITH n1, n2, COUNT(*) AS ignored
RETURN COUNT(*) AS nCombos;