A variable is a unique name (identifier) assigned to represent a collection of data of a specific type. Variables allow users to reference these data throughout the query, enabling data retrieval, manipulation, and further operations.

Graph Pattern Variables

Graph pattern variables include:

• Element Variable
  • Node Variable
  • Edge Variable
• Path Variable

These variables can be declared at specific places within path patterns, allowing them to be bound to nodes, edges, or paths that match the pattern.

In this query, n is a node variable bound to a list of nodes, e is an edge variable bound to a list of edges, p is a path variable that holds a path binding:

MATCH p = (:User {_id: "U01"})<-[e:Follows]-(n:User)
RETURN n, e, p

LET Variable Definition

The LET statement allows you to define variables which effectively adds columns to the binding table.

LET i = 2
RETURN i + 1

Unreferenced Variables

It is generally a good practice to remove any unreferenced variables from the query. For example,

MATCH (a)-[e]->(b)
RETURN e

If you don't need to reference the nodes bound to a and b, you can rewrite the query as:

MATCH ()-[e]->()
RETURN e

Unreferenced variables do not cause syntax errors but can lead to inefficiencies and reduced readability. It is best to avoid declaring variables you do not intend to use.