6615a9de53
Reviewers: buda Reviewed By: buda Subscribers: pullbot, mferencevic Differential Revision: https://phabricator.memgraph.io/D1547
1.6 KiB
Reading and Writing
OpenCypher supports combining multiple reads and writes using the
WITH clause. In addition to combining, the MERGE clause is provided which
may create patterns if they do not exist.
WITH
The write part of the query cannot be simply followed by another read part. In
order to combine them, WITH clause must be used. The names this clause
establishes are transferred from one part to another.
For example, creating a node and finding all nodes with the same property.
CREATE (node {property: 42}) WITH node.property AS propValue
MATCH (n {property: propValue}) RETURN n
Note that the node is not visible after WITH, since only node.property
was carried over.
This clause behaves very much like RETURN, so you should refer to features
of RETURN.
MERGE
The MERGE clause is used to ensure that a pattern you are looking for exists
in the database. This means that if the pattern is not found, it will be
created. In a way, this clause is like a combination of MATCH and CREATE.
Example. Ensure that a person has at least one friend.
MATCH (n :Person) MERGE (n)-[:FriendOf]->(m)
The clause also provides additional features for updating the values depending
on whether the pattern was created or matched. This is achieved with ON CREATE and ON MATCH sub clauses.
Example. Set a different properties depending on what MERGE did.
MATCH (n :Person) MERGE (n)-[:FriendOf]->(m)
ON CREATE SET m.prop = "created" ON MATCH SET m.prop = "existed"
For more details, click this link.