GraphGists

How to Compose Large Statements

Let’s first get some data in to retrieve results from:

CREATE (matrix:Movie {title:"The Matrix",released:1997})
CREATE (cloudAtlas:Movie {title:"Cloud Atlas",released:2012})
CREATE (forrestGump:Movie {title:"Forrest Gump",released:1994})
CREATE (keanu:Person {name:"Keanu Reeves", born:1964})
CREATE (robert:Person {name:"Robert Zemeckis", born:1951})
CREATE (tom:Person {name:"Tom Hanks", born:1956})
CREATE (tom)-[:ACTED_IN {roles:["Forrest"]}]->(forrestGump)
CREATE (tom)-[:ACTED_IN {roles:['Zachry']} ]->(cloudAtlas)
CREATE (robert)-[:DIRECTED]->(forrestGump)

Combine statements with UNION

A Cypher statement is usually quite compact. Expressing references between nodes as visual patterns makes them easy to understand.

If you want to combine the results of two statements that have the same result structure, you can use UNION [ALL].

For instance if you want to list both actors and directors without using the alternative relationship-type syntax ()-[:ACTED_IN|:DIRECTED]→() you can do this:

MATCH (actor:Person)-[r:ACTED_IN]->(movie:Movie)
RETURN actor.name AS name, type(r) AS acted_in, movie.title AS title
UNION
MATCH (director:Person)-[r:DIRECTED]->(movie:Movie)
RETURN director.name AS name, type(r) AS acted_in, movie.title AS title

Use WITH to Chain Statements

In Cypher it’s possible to chain fragments of statements together, much like you would do within a data-flow pipeline. Each fragment works on the output from the previous one and its results can feed into the next one.

You use the WITH clause to combine the individual parts and declare which data flows from one to the other. WITH is very much like RETURN with the difference that it doesn’t finish a query but prepares the input for the next part. You can use the same expressions, aggregations, ordering and pagination as in the RETURN clause.

The only difference is that you must alias all columns as they would otherwise not be accessible. Only columns that you declare in your WITH clause is available in subsequent query parts.

See below for an example where we collect the movies someone appeared in, and then filter out those which appear in only one movie.

MATCH (person:Person)-[:ACTED_IN]->(m:Movie)
WITH person, count(*) as appearances, collect(m.title) as movies
WHERE appearances > 1
RETURN person.name, appearances, movies

Tip: If you want to filter by an aggregated value in SQL or similar languages you would have to use HAVING. That’s a single purpose clause for filtering aggregated information. In Cypher, WHERE can be used in both cases.