LET

Overview

The LET statement allows you to define new variables and adds corresponding columns to the intermediate result table. Each variable is assigned a value using the = operator.

Syntax
<let statement> ::= 
  "LET" <let variable definition> [ { "," <let variable definition> }... ]

<let variable definition> ::= 
  <variable> "=" <value expression>

Details

• LET adds new columns to the intermediate result table without changing the number of rows.
• Re-defining an existing variable in LET overwrites its value.
• Variables defined in the same LET cannot reference each other.

Example Graph

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

GQL
INSERT (p1:Paper {_id:'P1', title:'Efficient Graph Search', score:6}),
       (p2:Paper {_id:'P2', title:'Optimizing Queries', score:9}),
       (p3:Paper {_id:'P3', title:'Path Patterns', score:7}),
       (p1)-[:Cites]->(p2),
       (p2)-[:Cites]->(p3)

Defining Variables

GQL
LET threshold = 7
MATCH (p:Paper) WHERE p.score > threshold
RETURN p.title, p.score - threshold

Result:

Using Queries in LET

You can assign the result of a subquery to a variable using VALUE { ... }:

GQL
MATCH (p:Paper)
LET avgScore = VALUE { MATCH (p2:Paper) RETURN avg(p2.score) }
FILTER p.score > avgScore
RETURN p.title, p.score

Result:

Referencing Variables in LET

If any variable is referenced in LET, it will be evaluated it row by row.

This query references x in LET and determines whether its score property is greater than 7:

GQL
MATCH (x:Paper)
LET recommended = x.score > 7
RETURN x.title, recommended

It is equivalent to:

GQL
MATCH (x:Paper)
CALL (x) {
  LET recommended = x.score > 7
  RETURN x, recommended
}
RETURN x.title, recommended

Result: