Composing large statements
1. Example graph
We continue using the same example data as before:
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)
This is the resulting graph:
2. UNION
If you want to combine the results of two statements that have the same result structure, you can use UNION [ALL]
.
For example, the following statement lists both actors and directors:
MATCH (actor:Person)-[r:ACTED_IN]->(movie:Movie)
RETURN actor.name AS name, type(r) AS type, movie.title AS title
UNION
MATCH (director:Person)-[r:DIRECTED]->(movie:Movie)
RETURN director.name AS name, type(r) AS type, movie.title AS title
Rows: 3 +-------------------------------------------------+ | name | type | title | +-------------------------------------------------+ | 'Tom Hanks' | 'ACTED_IN' | 'Cloud Atlas' | | 'Tom Hanks' | 'ACTED_IN' | 'Forrest Gump' | | 'Robert Zemeckis' | 'DIRECTED' | 'Forrest Gump' | +-------------------------------------------------+
Note that the returned columns must be aliased in the same way in all the sub-clauses.
The query above is equivalent to this more compact query:
|
3. WITH
In Cypher it is possible to chain fragments of statements together, similar to how it is done within a data-flow pipeline.
Each fragment works on the output from the previous one, and its results can feed into the next one.
Only columns declared in the WITH
clause are available in subsequent query parts.
The WITH
clause is used to combine the individual parts and declare which data flows from one to the other.
WITH
is similar to the RETURN
clause.
The difference is that the WITH
clause does not finish the query, but prepares the input for the next part.
Expressions, aggregations, ordering and pagination can be used in the same way as in the RETURN
clause.
The only difference is all columns must be aliased.
In the example below, 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
Rows: 1 +-------------------------------------------------------------+ | person.name | appearances | movies | +-------------------------------------------------------------+ | 'Tom Hanks' | 2 | ['Cloud Atlas', 'Forrest Gump'] | +-------------------------------------------------------------+
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