CODEWITHSUNDEEP
neo4jcypher
Khanetor
Khanetor

Reputation: 12304

Left join in Neo4j does not seem to work

This is my graph enter image description here

I am trying to make a query that tells me if the connections from a node of type T exist to nodes of type M. I heard that OPTIONAL MATCH is equivalent to SQL Left Join, but it does not include the the missing link.

Here is my attempt:

START t=node(241)
OPTIONAL MATCH t-[r:R]->(m)
RETURN m.name, r is not  NULL

and the result only has nodes M1, M2, M3. enter image description here

I also want to include the row M4 | false in the result.

If I modify the query a bit

START t=node(241), m=node(246,247, 248, 249)
OPTIONAL MATCH t-[r:R]->(m)
RETURN m.name, r is not  NULL

then I can get the desirable result, but it requires me to know the ids of all the M nodes in advance.

Upvotes: 2

Views: 1097

Answers (1)

Khanetor
Khanetor

Reputation: 12304

I felt kinda dump because I found the answer right after posting this.

All I need is an extra match to get all M nodes.

START t=node(241)
MATCH (m:M)
OPTIONAL MATCH t-[r:R]->(m)
RETURN m.name, r is not  NULL

Upvotes: 3

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