The COALESCE expression is a conditional expression that returns the first non-null value from a list of provided expressions. This is useful for substituting a default value when encountering null values, especially in scenarios where you want to avoid null results in calculations or display.

<coalesce expression> ::= 
  "COALESCE" "(" <value expression> { "," <value expression> }... ")"

The COALESCE(V1, V2, V3) expression is equivalent to the following CASE expression:

CASE 
  WHEN NOT V1 IS NULL THEN V1
  WHEN NOT V2 IS NULL THEN V2
  ELSE V3
END

Example Graph

The following examples run against this graph:

To create this graph, run the following query against an empty graph:

INSERT (p1:Paper {_id:'P1', title:'Efficient Graph Search', score:6, author:'Alex', publisher:'PulsePress'}),
       (p2:Paper {_id:'P2', title:'Optimizing Queries', score:9, author:'Alex'}),
       (p3:Paper {_id:'P3', title:'Path Patterns', score:7, author:'Zack', publisher:'BrightLeaf'}),
       (p1)-[:Cites {weight:2}]->(p2),
       (p2)-[:Cites {weight:1}]->(p3)

Example

MATCH (n:Paper)
RETURN n.title, COALESCE(n.publisher, "N/A") AS publisher

Result: