Cypher UNION - How to apply to collected lists

user_348545 0
Viewed 39

Consider the following use of UNION cypher command:

MATCH (user:User)-[]-(org:Organization)
WHERE org.size > 100
RETURN collect({
   user.name,
   user.age
}) AS userList

UNION

MATCH (user:User)-[]-(family:Family)
WHERE family.mood = "Happy"
RETURN collect({
   user.name,
   user.age
}) AS userList

The UNION does not work, this query returns users only from the first MATCH. I suspect it's because of the collect statements, however the project's design requires the data to be collected. Is there a way to create a union of the collections, or perhaps collect after the union?

cypher neo4j
2 Answers

You can use apoc.coll.union of the APOC library, to create a union of two lists, like this:

MATCH (user:User)-[]-(org:Organization)
WHERE org.size > 100
WITH collect({
   user.name,
   user.age
}) AS userList1
MATCH (user:User)-[]-(family:Family)
WHERE family.mood = "Happy"
WITH userList1, collect({
   user.name,
   user.age
}) AS userList2
RETURN apoc.coll.union(userList1, userList2) AS userList

The function apoc.coll.union will not include duplicates, if you want to include duplicates use apoc.coll.unionAll.

user_123681540

Your query will work just fine except that you should 1) return a valid dictionary format and 2) use CALL which is a subquery for neo4j cypher.

RETURN  {
   name: user.name,
   age:  user.age
   } AS userList

See sample below:

CALL {MATCH (user:user{id:"some_id"}) 
RETURN {
  id: user.id, 
  age: user.age
}  AS userList
UNION
MATCH (user:user{id:"some_id2"}) 
RETURN  {
  id: user.id, 
  age: user.age
}  AS userList
} 
RETURN collect(userList) as userList

 Result:
╒══════════════════════════════════════════════════════════╕
│"userList"                                                │
╞══════════════════════════════════════════════════════════╡
│[{"id":"some_id","age":null},{"id":"some_id2","age":null}]│
└──────────────────────────────────────────────────────────┘

I am using neo4j version 4.4.3

user_73718930
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