MERGE

MERGE matches an existing pattern or creates it if it doesn't exist. It's an idempotent "get or create" operation.

Basic Usage

MERGE (n:Person {name: "Alice"})
RETURN n

If a Person node with name: "Alice" exists, it is returned. Otherwise, one is created.

MERGE with Properties

MERGE (n:Person {name: "Alice"})
SET n.last_seen = "2024-01-15"
RETURN n

The SET clause runs whether the node was matched or created.

MERGE Edges

MATCH (a:Person {name: "Alice"}), (b:Person {name: "Bob"})
MERGE (a)-[:KNOWS]->(b)

This creates the KNOWS edge only if it doesn't already exist.

Use Cases

MERGE is useful when:

• Importing data that may have duplicates
• Ensuring a relationship exists without creating duplicates
• Building graphs incrementally from multiple data sources