Joining two subqueries with Cypher in Neo4J

Question

I have a following SQL query:

SELECT q1.customerId, q1.invoiceId, q2.workId, sum(q2.price)
FROM (select customer.id as customerId, invoice.id as invoiceId, work.id as workId from customer, invoice, workinvoice, work where customer.id=invoice.customerid and invoice.id=workinvoice.invoiceId and workinvoice.workId=work.id
) as q1, (select work.id as workId, sum((price * hours * workhours.discount) + (purchaseprice * amount * useditem.discount)) as price from worktype,workhours,work,warehouseitem,useditem where worktype.id=workhours.worktypeid and workhours.workid=work.id and work.id=useditem.workid and useditem.warehouseitemid=warehouseitem.id group by work.id
) as q2
WHERE q1.workId = q2.workId group by q1.invoiceId;

This query should return me a sum of work prices for each invoice per customer.

I would be interested to know how to do this kind of query in Neo4J. I know that there is UNION https://neo4j.com/docs/cypher-manual/current/clauses/union/ . However that does seem to do what I want. I need to make two subqueries and join them from same node as in that SQL example. What would be the correct way to do this with Cypher?

Answer 1

There's a quite complex example of how to do a join in cypher which you can find here: https://github.com/moxious/halin/blob/master/src/api/data/queries/dbms/3.5/tasks.js#L22

Basically, the technique is that you run the first query, collect the results. Then you run the second, collect the results. Then you unwind the second, match using a filter, and return the result.

In really simplified form, it looks something like this:

CALL something() YIELD a, b
WITH collect({ a: a, b: b }) as resultSet1
CALL somethingElse YIELD a, c
WITH resultSet1, collect({ a: a, c: c }) as resultSet2

UNWIND resultSet2 as rec
WITH [item in resultSet1 WHERE item.a = rec.a][0] as match, rec

RETURN match.a, match.b, rec.c

The list comprehension bit is basically doing the join. Here we're joining on the "a" field.

Answer 2

I figured out the solution I wanted:

MATCH (inv:invoice)-[:WORK_INVOICE]->(w:work)<-[h:WORKHOURS]-(wt:worktype) WITH inv, w, SUM(wt.price * h.hours * h.discount) as workTimePrice OPTIONAL MATCH (w)-[u:USED_ITEM]->(i:item) WITH inv, workTimePrice + SUM(u.amount * u.discount * i.purchaseprice) as workItemPrice RETURN inv, sum(workItemPrice) as invoicePrice