Overview

The GROUP BY clause allows you to specify the set of grouping keys to be used during grouping on the final table.

<return statement> ::= 
  "RETURN" [ "DISTINCT" ] { <"*"> | <return item list> }
  [ <group by clause> ]
                                 
<group by clause> ::= "GROUP BY" <grouping key list>

<grouping key list> ::=
    <grouping key> [ { "," <grouping key> }... ]

<grouping key> ::= <binding variable>

Details

• Each grouping key must be a binding variable. If the desired grouping key is not already an existing binding variable, you have two options:
  • Renaming using AS: If the grouping key is part of the final result table, you can rename the corresponding column using the AS keyword.
  • Using LET: Alternatively, you can use the LET statement to define a new variable for the grouping key before the RETURN statement, ensuring it is available for grouping.
• After grouping, only one record in each group will be returned.
• When grouping is involved, any aggregation operation in the RETURN statement is applied to each group after the grouping is done.

Example Graph

The following examples run against this graph:

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

INSERT (alex:Student {_id: 's1', name: 'Alex', gender: 'male'}),
       (susan:Student {_id: 's2', name: 'Susan', gender: 'female'}),
       (alex2:Student {_id: 's3', name: 'Alex', gender: 'female'}),
       (art:Course {_id: 'c1', name: 'Art', credit: 13}),
       (literature:Course {_id: 'c2', name: 'Literature', credit: 15}),
       (alex)-[:Take {year: 2024, term: 'Spring'}]->(art),
       (alex2)-[:Take {year: 2023, term: 'Fall'}]->(art),
       (susan)-[:Take {year: 2023, term: 'Fall'}]->(art),
       (susan)-[:Take {year: 2023, term: 'Spring'}]->(literature)

Grouping by One Key

MATCH (:Student)->(c:Course)
RETURN c GROUP BY c

Result: c

Grouping by Column Alias

In this query, the grouping key Name is the column alias of n.name:

MATCH (n:Student)
RETURN n.name AS Name GROUP BY Name

Result:

The following query throws syntax error as the grouping key n.name is not a binding variable:

MATCH (n:Student)
RETURN n.name GROUP BY n.name

Grouping by Variables Defined by LET

In this query, the grouping key Gender is defined by the LET statement:

MATCH (n:Student)
LET Gender = n.gender
RETURN n GROUP BY Gender

Result:

The following query throws syntax error as the grouping key n.gender is not a binding variable:

MATCH (n:Student)
RETURN n GROUP BY n.gender

Grouping with Aggregation

MATCH (n:Student)
RETURN n.name AS Name, count(n) GROUP BY Name

Result:

Grouping by Multiple Keys

MATCH ({_id: "c1"})<-[e:Take]-()
RETURN e.year AS Y, e.term AS T GROUP BY Y, T

Result: