Neo4J Cypher: Match ()-[]-() Return count(*) 未分配节点标签时返回关系数的两倍

Question

In my database, there is a kind of relationships between A and B named awithb . For the Cypher

MATCH ()-[:awithb]-() return count(*)

it returns 140.

However if we give the labels of the node,

MATCH (:A)-[:awithb]-(:B) return count(*)

it returns 70.

Why these two cypher queries return different results?

Answer 1

Cypher is about returning paths that match patterns.

Paths are ordered sequences of nodes and relationships, and when no direction is specified, and no labels are specified, then a pattern like that will produce two paths using the same relationship and the same two nodes, just the order of the nodes in the path is different, and you traverse the relationship in the other direction.

If you add a direction to the pattern, then only one path is possible:

MATCH ()-[:awithb]->() 
RETURN count(*)

Answer 2

When you put no labels on your query, it means that you want ANY nodes that have that relationship.

 () - [: awithb] - ()  where () is any nodes 

When you put non-directional path with corresponding labels; it means the relationship can be from A to B or B to A.

 (:A) - [: awithb] - (:B) equals  A->B  OR  A<-B

Thus, in your first query, you are getting 2x the counts because you are getting the path from A to B and B to A.