How to find node with no incoming relationship in neo4j

Question

I am having 2 node types lets say of type 'Student' and 'Teacher'

Student have {id, name}.
Teacher have {id, name}.

Student can have optional relationship with Class node as 'TEACHES'.

(t:Teacher)-[r:TEACHES]->(c:Student).

[r:TEACHES] - Optional relationship. (present or may not present)

I want to find "Student" nodes who don't have teacher. i.e There is no any incoming relationship "TEACHES"

Please help.

score 11 · Answer 1 · answered Apr 21 '14 at 13:03

11

I think you're looking for this sort of pattern.

MATCH (s:Student)
WHERE NOT (s)<-[:TEACHES]-(:Teacher)
RETURN s

answered Apr 21 '14 at 13:03

Eve Freeman

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score 6 · Accepted Answer · edited Apr 21 '14 at 14:03

6

Here's a simple data setup, along with the query at the bottom you need to solve your problem. Essentially, you want to query for situations where a relationship doesn't exist. The syntax here is for neo4j 2.0, so the answer would be slightly different for older versions.

neo4j-sh (?)$ create (t:Teacher {name:"Bob"})-[r:TEACHES]->(s:Student {name:"Mary"});
+-------------------+
| No data returned. |
+-------------------+
Nodes created: 2
Relationships created: 1
Properties set: 2
Labels added: 2
19 ms

neo4j-sh (?)$ create (t:Teacher {name:"Mark"});
+-------------------+
| No data returned. |
+-------------------+
Nodes created: 1
Properties set: 1
Labels added: 1
5 ms

neo4j-sh (?)$ MATCH (s:Student) WHERE NOT (s)<-[:TEACHES]-(:Teacher) RETURN s

edited Apr 21 '14 at 14:03

Somnath Muluk

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answered Apr 21 '14 at 12:13

FrobberOfBits

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I wanted to find "Student" nodes who don't have teacher. Thanks for help. – Somnath Muluk Apr 21 '14 at 12:51
Just run the query in the opposite direction: match (s:Student) where not (s)<-[:TEACHES]-() return s; – FrobberOfBits Apr 21 '14 at 13:07

score 1 · Answer 3 · answered Apr 21 '14 at 12:50

1

I got result by this. First match student criteria and then find relationship is null

MATCH (s:Student)
OPTIONAL MATCH (t:Teacher)-[r:TEACHES]->(s)
WITH s,r
WHERE r IS NULL
RETURN s.name

answered Apr 21 '14 at 12:50

Somnath Muluk

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You could profile this query and compare to Wes', I think his is probably more straightforward (and I'd drop the `:Teacher` label unless you have non-teacher nodes that also `-[:TEACH]->` student-nodes). – jjaderberg Apr 21 '14 at 17:30

How to find node with no incoming relationship in neo4j

3 Answers3