Overview

The LET statement allows you to add columns to the current working table by defining new variables. Each variable is assigned a value using the = operator.

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

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

Details

• LET does not change the number of records of the working table.
• LET does not modify existing columns of the working table unless you redefine existing variables within LET.
• You cannot define a new variable and reference it within the same LET.
• If any existing variable is referenced in <value expression>s within LET, the LET statement is effectively replaced by the statement CALL (IBVRL) { BVDB RETURN RIL }, where,
  • IBVRL (Incoming Binding Variables Reference) is the comma-separated list of all variables referenced in <value expression>s.
  • BVDB (Binding Variable Definition Block) is the space-separated concatenation of all <let variable definition>s.
  • RIL (Return Item List) is the comma-separated list of all <binding variable>s.

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'}),
       (p2:Paper {_id:"P2", title:'Optimizing Queries', score:9, author:'Alex'}),
       (p3:Paper {_id:"P3", title:'Path Patterns', score:6, author:'Zack'}),
       (p1)-[:Cites]->(p2),
       (p2)-[:Cites]->(p3)

Defining Variables with Constants

LET s = 6, a = "Alex"
MATCH (p:Paper) WHERE p.score = s AND p.author = a
RETURN p.title, s, a

Result:

Defining Variables with Existing Variables

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

Result:

MATCH p = ()->{1,2}()
LET length = path_length(p)
RETURN p, length

Result: