CREATE UNIQUE is used to describe the pattern that should be found or created.

Query

START left=node(1), right=node(3,4)
CREATE UNIQUE left-[r:KNOWS]->right
RETURN r

The left node is matched agains the two right nodes. One relationship already exists and can be matched, and the other relationship is created before it is returned.

Try this query live. (1) {"name":"A"} (2) {"name":"root"} (3) {"name":"B"} (4) {"name":"C"} (1)-[:KNOWS]->(4) {} (1)-[:KNOWS]->(3) {} (2)-[:X]->(1) {} (2)-[:X]->(3) {} (2)-[:X]->(4) {} start left=node(1), right=node(3,4) create unique left-[r:KNOWS]->right return r

If the pattern described needs a node, and it can’t be matched, a new node will be created.

Query

START root=node(2)
CREATE UNIQUE root-[:LOVES]-someone
RETURN someone

The root node doesn’t have any LOVES relationships, and so a node is created, and also a relationship to that node.

Try this query live. (1) {"name":"A"} (2) {"name":"root"} (3) {"name":"B"} (4) {"name":"C"} (5) {} (1)-[:KNOWS]->(4) {} (2)-[:X]->(1) {} (2)-[:X]->(3) {} (2)-[:X]->(4) {} (5)-[:LOVES]->(2) {} start root=node(2) create unique root-[:LOVES]-someone return someone

The pattern described can also contain values on the node. These are given using the following syntax: prop : <expression>.

Query

START root=node(2)
CREATE UNIQUE root-[:X]-(leaf {name:'D'} )
RETURN leaf

No node connected with the root node has the name D, and so a new node is created to match the pattern.

Try this query live. (1) {"name":"A"} (2) {"name":"root"} (3) {"name":"B"} (4) {"name":"C"} (5) {"name":"D"} (1)-[:KNOWS]->(4) {} (2)-[:X]->(1) {} (2)-[:X]->(3) {} (2)-[:X]->(4) {} (5)-[:X]->(2) {} start root=node(2) create unique root-[:X]-(leaf {name:'D'} ) return leaf

Relationships to be created can also be matched on values.

Query

START root=node(2)
CREATE UNIQUE root-[r:X {since:'forever'}]-()
RETURN r

In this example, we want the relationship to have a value, and since no such relationship can be found, a new node and relationship are created. Note that since we are not interested in the created node, we don’t name it.

Try this query live. (1) {"name":"A"} (2) {"name":"root"} (3) {"name":"B"} (4) {"name":"C"} (5) {} (1)-[:KNOWS]->(4) {} (2)-[:X]->(1) {} (2)-[:X]->(3) {} (2)-[:X]->(4) {} (5)-[:X]->(2) {"since":"forever"} start root=node(2) create unique root-[r:X {since:'forever'}]-() return r

The pattern described by CREATE UNIQUE can be separated by commas, just like in MATCH and CREATE.

Query

START root=node(2)
CREATE UNIQUE root-[:FOO]->x, root-[:BAR]->x
RETURN x

This example pattern uses two paths, separated by a comma.

Try this query live. (1) {"name":"A"} (2) {"name":"root"} (3) {"name":"B"} (4) {"name":"C"} (5) {} (1)-[:KNOWS]->(4) {} (2)-[:X]->(1) {} (2)-[:X]->(3) {} (2)-[:X]->(4) {} (2)-[:FOO]->(5) {} (2)-[:BAR]->(5) {} start root=node(2) create unique root-[:FOO]->x, root-[:BAR]->x return x