[SOLVED] Query to return nodes with incoming edges but exclude nodes that also have outgoing edges of the same edge type

Query to return nodes with incoming edges but exclude nodes that also have outgoing edges of the same edge type

I have a database formatted like this:

(a:Concept)-[r:BROADER_TERM]->(b:Concept)-[s:BROADER_TERM]->(c:Concept)-[t:RELATED_TERM]->(d:Concept)

I'd like to write a query that returns Concept nodes that only have incoming BROADER_TERM edges and excludes any node that has both incoming and outgoing BROADER_TERM edges (ie I want to return the 'broadest term'). In the example above, it would be a query that only returns node c.

I tried something like this:

MATCH (a:Concept)-[r:BROADER_TERM]->(b)
WHERE NOT (b)-[r]->(c:Concept)
RETURN b

But I can't introduce a new variable in the WHERE NOT clause.

Can someone show me the correct syntax for this type of query?

Solution

This query will find all the "broadest" concepts (i.e., Concept nodes that have no broader concepts):

MATCH (c:Concept)
WHERE NOT (c)-[:BROADER_TERM]->()
RETURN c

But if you really want to show the "broadest" concepts that have at least one "lesser" concept:

MATCH (c:Concept)
WHERE NOT (c)-[:BROADER_TERM]->() AND ()-[:BROADER_TERM]->(c)
RETURN c

Note: NOT has higher precedence than AND, so the NOT above only applies to (c)-[:BROADER_TERM]->().