MATCH

Overview

The MATCH statement allows you to specify a graph pattern to search for in the graph. It is the fundamental statement for retrieving data from the graph database and binding them to variables for use in subsequent parts of the query.

Example Graph

CREATE GRAPH myGraph { 
  NODE User ({name string}),
  NODE Club ({since uint32}),
  EDGE Follows ()-[{createdOn date}]->(),
  EDGE Joins ()-[{memberNo uint32}]->()
}

INSERT (rowlock:User {_id: 'U01', name: 'rowlock'}),
       (brainy:User {_id: 'U02', name: 'Brainy'}),
       (purplechalk:User {_id: 'U03', name: 'purplechalk'}),
       (mochaeach:User {_id: 'U04', name: 'mochaeach'}),
       (lionbower:User {_id: 'U05', name: 'lionbower'}),
       (c01:Club {_id: 'C01', since: 2005}),
       (c02:Club {_id: 'C02', since: 2005}),
       (rowlock)-[:Follows {createdOn: '2024-01-05'}]->(brainy),
       (mochaeach)-[:Follows {createdOn: '2024-02-10'}]->(brainy),
       (brainy)-[:Follows {createdOn: '2024-02-01'}]->(purplechalk),
       (purplechalk)-[:Follows {createdOn: '2024-05-03'}]->(lionbower),
       (brainy)-[:Joins {memberNo: 1}]->(c01),
       (lionbower)-[:Joins {memberNo: 2}]->(c01),
       (mochaeach)-[:Joins {memberNo: 9}]->(c02)

Matching All Nodes

MATCH (n)
RETURN n

Result: n

Matching All Edges

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

Result: e

Notice that if you don't specifiy the edge direction, either as outgoing or incoming, each edge in the graph will be returned twice, as two paths are considered distinct when their element sequences differ, i.e., (n1)-[e]->(n2) and (n2)<-[e]-(n1) are different paths.

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

Matching with Labels/Schema

Both node pattern and edge pattern support the label/schema expression to specify schemas (in typed graphs) or labels (in open graphs).

To retrieve all Club nodes:

MATCH (n:Club)
RETURN n

Result: n

To retrieve all nodes connected to Brainy with Follows or Joins edges:

MATCH (:User {name: 'Brainy'})-[:Follows|Joins]-(n)
RETURN n

Result: n

Matching with Property Specification

Property specification can be included in node and edge patterns to apply joint equalities to filter nodes and edges with key-value pairs.

To retrieve Club nodes whose _id and since have specific values:

MATCH (n:Club {_id: 'C01', since: 2005})
RETURN n

Result: n

To retrieve the name of the member of club C01 whose memberNo is 1:

MATCH (:Club {_id: 'C01'})<-[:Joins {memberNo: 1}]-(n)
RETURN n.name

Result: n

Matching with Abbreviated Edges

You can use abbreviated edge patterns when you do not need to filter edges or assign them to a variable. Even with the abbreviated form, you may still specify the direction of the edge when necessary.

To retrieve nodes connected with mochaeach with any outgoing edges:

MATCH (:User {name: 'mochaeach'})->(n)
RETURN n

Result: n

Matching Paths

To retrieve users followed by mochaeach, and the clubs joined by those users:

MATCH p = (:User {name: 'mochaeach'})-[:Follows]->(:User)-[:Joins]->(:Club)
RETURN p

Result: p

Matching with WHERE Clauses

The WHERE clause can be used within an element pattern (node or edge pattern), a parenthesized path pattern, or immediately after a graph pattern in the MATCH statement to specify various search conditions.

Element Pattern WHERE Clause

To retrieve 1-step paths with outgoing Follows edges, where their createdOn values are greater than a specified date:

MATCH p = ()-[e:Follows WHERE e.createdOn > '2024-04-01']->()
RETURN p

Result: p

Parenthesized Path Pattern WHERE Clause

To retrieve one- or two-step paths containing outgoing Follows edges, where their createdOn values are smaller than a specified value:

MATCH p = (()-[e:Follows]->() WHERE e.createdOn < "2024-02-05"){1,2}
RETURN p

Result: p

Graph Pattern WHERE Clause

To retrieve members of club C01 whose memberNo is greater than 1:

MATCH (c:Club)<-[e:Joins]->(n)
WHERE c._id = 'C01' AND e.memberNo > 1
RETURN n

Result: n

Matching Quantified Paths

A quantified path is a variable-length path where the complete path or a part of it is repeated a specified number of times.

To retrieve distinct nodes related to lionbower in 1 to 3 hops:

MATCH (:User {name: 'lionbower'})-[]-{1,3}(n)
RETURN collect_list(DISTINCT n._id) AS IDs

Result:

To retrieve paths that begin with one- or two-step subpaths containing Follows edges, where their createdOn values are greater than a specified value, and these subpaths must connect to node C01:

MATCH p = (()-[e:Follows]->() WHERE e.createdOn > "2024-01-31"){1,2}()-({_id:"C01"})
RETURN p

Result: p

Matching Shortest Paths

A shortest paths between two nodes are the paths that has the fewest edges.

To retrieve all the shortest paths between lionbower and purplechalk within 5 hops:

MATCH p = ALL SHORTEST (n1:User)-[]-{,5}(n2:User)
WHERE n1.name = 'lionbower' AND n2.name = 'purplechalk'
RETURN p

Result: p

Matching Connected Paths

When the MATCH statement contains two or more path patterns which are connected by common elements, the final result is produced by taking the equi-join on the common element variables of the result sets from the different path patterns.

To retrieve Club nodes (y) which are connected with nodes (x) that have relationships with both rowlock and purplechalk:

MATCH ({name: 'rowlock'})-(x)-({name: 'purplechalk'}), (x)-[]-(y:Club)
RETURN y

Result: y

Matching Disconnected Paths

When the MATCH statement contains two or more disconnected path patterns (i.e., no common elements), the final result is produced by taking the Cartesian product of the result sets from the different path patterns.

To retrieve Club nodes, and User nodes who follow others after 2024-02-01:

MATCH (c:Club), (u:User)-[f:Follows WHERE f.createdOn > '2024-02-01']->()
RETURN c._id, u.name

Result:

MATCH YIELD

The YIELD clause can be used to select specific node, edge, or path variables from the MATCH statement, making them accessible for reference in subsequent parts of the query. Variables not selected with YIELD will no longer be available. If the YIELD clause is omitted, all variables are passed through by default.

This query only returns c, as n is not involved in YIELD:

MATCH (n:User)-[:Joins]->(c:Club)
YIELD c
RETURN *

Result: c

This query returns n1 and e, n2 is not included:

MATCH (n1:Club)
MATCH (n2:Club)<-[e:Joins WHERE e.memberNo < 3]-() YIELD e
RETURN *

n1

e

This query throws syntax error since n2 is not selected in the YIELD clause, thus it cannot be accessed by the RETURN statement:

MATCH (n1:User), (n2:Club)
YIELD n1
RETURN n1, n2