title: Neo4j: when merging does not overwrite node properties
body: <p>I want to modify a MERGE Cypher query so that the property field is not overwritten.</p>
  
  <p>To update the node properties I use the following cypher query:</p>
  
  <p><code>MERGE (n:Person {name:"me"})
  ON MATCH SET n+={id:"2"}
  ON CREATE SET n={name:"me", id="1"}
  RETURN n</code>   </p>
  
  <p>If I call the same query again with
  <code>ON MATCH SET n+={id:"3"}</code>
  the id will be updated.</p>
  
  <p>How to make a query that adds the property if it is not existing but does not overwrite it if it is already present?</p>