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I'm trying to figure out what is the difference between MERGE and CREATE UNIQUE. I know these features:
I'm able to create node, if doesn't exist pattern.
MERGE (n { name:"X" }) RETURN n;
This create node "n" with property name, empty node "m" and relationship RELATED.
MERGE (n { name:"X" })-[:RELATED]->(m) RETURN n, m;
I'm not able to create node like this.
CREATE UNIQUE (n { name:"X" }) RETURN n;
If exists node "n", create unique makes empty node "m" and relationship RELATED.
MATCH (n { name: 'X' }) CREATE UNIQUE (n)-[:RELATED]->(m) RETURN n, m;
If this pattern exists, nothing created, only returns pattern.
From my point of view, I see MERGE and CREATE UNIQUE are quite same queries, but with CREATE UNIQUE you can't create start node in relationship. I would be grateful, if someone could explain this issue and compare these queries, thx.
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MERGE command is a combination of CREATE command and MATCH command. Neo4j CQL MERGE command searches for a given pattern in the graph. If it exists, then it returns the results. If it does NOT exist in the graph, then it creates a new node/relationship and returns the results.
With UNWIND , you can transform any list back into individual rows.
Neo4j CQL CREATE a Node Label We can say this Label name to a Relationship as "Relationship Type". We can use CQL CREATE command to create a single label to a Node or a Relationship and multiple labels to a Node. That means Neo4j supports only single Relationship Type between two nodes.
An OPTIONAL MATCH matches patterns against your graph database, just like a MATCH does. The difference is that if no matches are found, OPTIONAL MATCH will use a null for missing parts of the pattern. OPTIONAL MATCH could be considered the Cypher equivalent of the outer join in SQL.
CREATE UNIQUE has slightly more obscure semantics than MERGE. MERGE was developed as an alternative with more intuitive behavior than CREATE UNIQUE; if in doubt, MERGE is usually the right choice.
The easiest way to think of MERGE is as a MATCH-or-create. That is, if something in the database would MATCH the pattern you are using in MERGE, then MERGE will just return that pattern. If nothing matches, the MERGE will create all missing elements in the pattern, where a missing element means any unbound identifier.
Given
MATCH (a {uid:123}) MERGE (a)-[r:LIKES]->(b)-[:LIKES]->(c) "a" is a bound identifier from the perspective of the MERGE. This means cypher somehow already knows which node it represents.
This statement can have two outcomes. Either the whole pattern already exists, and nothing will be created, or parts of the pattern are missing, and a whole new set of relationships and nodes matching the pattern will be created.
Examples
// Before merge: (a)-[:LIKES]->()-[:LIKES]->() // After merge: (a)-[:LIKES]->()-[:LIKES]->() // Before merge: (a)-[:LIKES]->()-[:OWNS]->() // After merge: (a)-[:LIKES]->()-[:OWNS]->() (a)-[:LIKES]->()-[:LIKES]->() // Before merge: (a) // After merge: (a)-[:LIKES]->()-[:LIKES]->() If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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