Cypher: How to return a node if the relationship doesn't exist?

问题

I have User and Building labels for nodes, the relationships are User-[:HAS_PERMISSION]->Building

To get all buildings that a user is having permissions to so I use MATCH (u:User {id: {id}}),(u)-[r:HAS_PERMISSION]->(b:Building) return b

How can I just return the user in case he exists and there are no relationships? (basically I also want to know if the user exists at all..)

回答1:

Not sure if I understand your question correctly, but I think you'll need an OPTIONAL MATCH. This query shows all users with or without access to a building.

MATCH (u:User)
OPTIONAL MATCH (u)-[r:HAS_PERMISSION]->(b:Building) 
RETURN u, b

Or maybe your requirement is simpler. If you just want all users, there's no need to use pattern matching:

MATCH (u:User)
RETURN u

来源：https://stackoverflow.com/questions/22484598/cypher-how-to-return-a-node-if-the-relationship-doesnt-exist