Using match and exists to check if a relationship exists

[arunkumar413]

Hi Team,

I'd like to check if a (User) node has a -[:relationship]-> with Group node. Should I just use MATCH or both MATCH and EXISTS to check if a relationship exists between to nodes with given unique ID.

Thanks,
Arun

[glilienfield · Accepted solution]

In the case of using a 'match pattern', execution will require to determine all 'group' nodes attached to the 'user' node and capture them for output. In the case of using an 'exists' predicate, all that is required by the execution is to find the existence of just one relationships to a 'group' node. The search can stop after finding the first relationship to a 'group' node. The output is also simpler, as on the 'user' node will be returned, while in the 'match pattern' approach, a row for each 'group' node will be returned.

considering you are just interested in the existence of the relationship, and not the 'relationship' nor 'group' properties, the 'match/exists' approach meets your needs and seems more efficient.

[arunkumar413]

In the examples listed under the EXISTS() function MATCH is also used.

Neo4j Graph Data Platform

Predicate functions - Neo4j Cypher Manual

Predicates are boolean functions that return `true` or `false` for a given set of non-`null` input.

particularly the below statements matches all node

MATCH (n)
WHERE exists(n.name)
RETURN
  n.name AS name,
  exists((n)-[:MARRIED]->()) AS is_married

[hunkim]

Wow! This is a perfect solution. However, it may be slow when we have many nodes and relationships. Should we add an index on relationships or nodes with the name to make it faster?