MERGE

The MERGE clause ensures that a pattern exists in the graph. Either the pattern already exists, or it needs to be created.

MERGE either matches existing nodes, or creates new data. It’s a combination of MATCH and CREATE.

For example, you can specify that the graph must contain a node for a user with a certain name. If there isn’t a node with the correct name, a new node will be created and its name property set. When using MERGE on full patterns, the behavior is that either the whole pattern matches, or the whole pattern is created. MERGE will not partially use existing patterns. If partial matches are needed, this can be accomplished by splitting a pattern up into multiple MERGE clauses.

As with MATCH, MERGE can match multiple occurrences of a pattern. If there are multiple matches, they will all be passed on to later stages of the query.

Data Setup

SELECT * from cypher('graph_name', $$
CREATE (A:Person {name: "Charlie Sheen", bornIn: "New York"}),
    (B:Person {name: "Michael Douglas", bornIn: "New Jersey"}),
    (C:Person {name: "Rob Reiner", bornIn: "New York"}),
    (D:Person {name: "Oliver Stone", bornIn: "New York"}),
    (E:Person {name: "Martin Sheen", bornIn: "Ohio"})
$$) as (result agtype);

Merge Nodes

Merge a Node with a Label

By just specifying a pattern with a single vertex and no labels, all vertices in the graph will be returned.

Query

SELECT * FROM cypher('graph_name', $$
MERGE (v:Critic)
RETURN v
$$) as (v agtype);

If there exists a vertex with the label ‘Critic’, that vertex will be returned. Otherwise, the vertex will be created and returned.

v

{id: 0; label: ‘Critic’: properties:{}}::vertex

1 row(s) returned

Merge Single Vertex with Properties

Merging a vertex node with properties where not all properties match any existing vertex.

Query

SELECT * FROM cypher('graph_name', $$
MERGE (charlie {name: 'Charlie Sheen', age: 10})
RETURN charlie
$$) as (v agtype);

If there exists a vertex with the label ‘Critic’, that vertex will be returned. Otherwise, the vertex will be created and returned.

v

{id: 0; label: ‘Actor’: properties:{name: 'Charlie Sheen', age: 10}}::vertex

1 row(s) returned

If there exists a vertex with all properties, that vertex will be returned. Otherwise, a new vertex with the name ‘Charlie Sheen’ will be created and returned.

Merge a Single Vertex Specifying Both Label and Property

Merging a vertex where both label and property constraints match an existing vertex.

Query

SELECT * FROM cypher('graph_name', $$
MERGE (michael:Person {name: 'Michael Douglas'})
RETURN michael.name, michael.bornIn
$$) as (Name agtype, BornIn agtype);

‘Michael Douglas’ will match the existing vertex and the vertex’s name and bornIn properties will be returned.

Name	BornIn
"Michael Douglas"	"New Jersey"
1 row(s) returned