Order nodes by relationship count --> ThisShouldNotHappenError

12
votes

In a Neo4j database with a couple of nodes and relationships, I am trying to find out the most "popular" users (in this case: The nodes participating in most relationships):

START n=node:user('*:*')
MATCH (n)-[r]->(x)
RETURN n
ORDER BY COUNT(r) DESC
LIMIT 10

However, this query (Neo4j 1.9.2) results in the following error:

ThisShouldNotHappenError

Developer: Andres claims that: Aggregations should not be used like this.

StackTrace: org.neo4j.cypher.internal.commands.expressions.AggregationExpression.apply(AggregationExpression.scala:31) org.neo4j.cypher.internal.commands.expressions.AggregationExpression.apply(AggregationExpression.scala:29) org.neo4j.cypher.internal.pipes.ExtractPipe$$anonfun$internalCreateResults$1$$anonfun$apply$1.apply(ExtractPipe.scala:47) org.neo4j.cypher.internal.pipes.ExtractPipe$$anonfun$internalCreateResults$1$$anonfun$apply$1.apply(ExtractPipe.scala:45) scala.collection.immutable.Map$Map1.foreach(Map.scala:109) org.neo4j.cypher.internal.pipes.ExtractPipe$$anonfun$internalCreateResults$1.apply(ExtractPipe.scala:45) org.neo4j.cypher.internal.pipes.ExtractPipe$$anonfun$internalCreateResults$1.apply(ExtractPipe.scala:44) scala.collection.Iterator$$anon$11.next(Iterator.scala:328) org.neo4j.cypher.internal.pipes.TopPipe.internalCreateResults(TopPipe.scala:45) org.neo4j.cypher.internal.pipes.PipeWithSource.createResults(Pipe.scala:69) org.neo4j.cypher.internal.pipes.PipeWithSource.createResults(Pipe.scala:66) org.neo4j.cypher.internal.executionplan.ExecutionPlanImpl.org$neo4j$cypher$internal$executionplan$ExecutionPlanImpl$$prepareStateAndResult(ExecutionPlanImpl.scala:164) org.neo4j.cypher.internal.executionplan.ExecutionPlanImpl$$anonfun$getLazyReadonlyQuery$1.apply(ExecutionPlanImpl.scala:139) org.neo4j.cypher.internal.executionplan.ExecutionPlanImpl$$anonfun$getLazyReadonlyQuery$1.apply(ExecutionPlanImpl.scala:138) org.neo4j.cypher.internal.executionplan.ExecutionPlanImpl.execute(ExecutionPlanImpl.scala:38) org.neo4j.cypher.ExecutionEngine.execute(ExecutionEngine.scala:72) org.neo4j.cypher.ExecutionEngine.execute(ExecutionEngine.scala:76) org.neo4j.cypher.javacompat.ExecutionEngine.execute(ExecutionEngine.java:79) org.neo4j.server.rest.web.CypherService.cypher(CypherService.java:94) java.lang.reflect.Method.invoke(Method.java:611) org.neo4j.server.rest.security.SecurityFilter.doFilter(SecurityFilter.java:112)

Any ideas on how I can express this differntly?

2
neo4jcypher

2 Answers

20
votes

In terms of neo4j mannual, if you need to use an aggregration in your "Order by", you must include the aggregration in your "Return", so you just need to add the count(r) in your "Return" as shown below, 

START n=node:user('*:*')
MATCH (n)-[r]->(x)
RETURN n, COUNT(r)
ORDER BY COUNT(r) DESC
LIMIT 10
5
votes

Introduce a WITH here:

START n=node:user('*:*')
MATCH (n)-[r]->()
WITH n, count(r) as c
RETURN n, c
ORDER BY c DESC
LIMIT 10