10.3. Where

WHERE is not a clause in it’s own right — rather, it’s part of MATCH, OPTIONAL MATCH, START and WITH.

In the case of WITH and START, WHERE simply filters the results.

For MATCH and OPTIONAL MATCH on the other hand, WHERE adds constraints to the patterns described. It should not be seen as a filter after the matching is finished.

[Note]Note

In the case of multiple (OPTIONAL) MATCH clauses, the predicate in WHERE is always a part of the patterns in the directly preceding MATCH. Both results and performance may be impacted if the WHERE is put inside the wrong MATCH clause.

Figure 10.3. Graph

Basic usage

Boolean operations

You can use the expected boolean operators AND and OR, and also the boolean function NOT. See Section 8.10, “Working with NULL” for more information on how this works with NULL.

Query. 

MATCH (n)
WHERE n.name = 'Peter' XOR (n.age < 30 AND n.name = "Tobias") OR NOT (n.name = "Tobias" OR
  n.name="Peter")
RETURN n

This query shows how boolean operators can be used.

Result

n
3 rows

Node[0]{name:"Tobias",age:25}

Node[1]{name:"Peter",age:34}

Node[2]{name:"Andres",age:36,belt:"white"}

Try this query live. create (_0 {`age`:25, `name`:"Tobias"}) create (_1 {`age`:34, `name`:"Peter"}) create (_2:`Swedish` {`age`:36, `belt`:"white", `name`:"Andres"}) create _2-[:`KNOWS`]->_1 create _2-[:`KNOWS`]->_0 match (n) where n.name = 'Peter' xor (n.age < 30 and n.name = "Tobias") or not (n.name = "Tobias" or n.name="Peter") return n

Filter on node label

To filter nodes by label, write a label predicate after the WHERE keyword using WHERE n:foo.

Query. 

MATCH (n)
WHERE n:Swedish
RETURN n

The "Andres" node will be returned.

Result

n
1 row

Node[2]{name:"Andres",age:36,belt:"white"}

Try this query live. create (_0 {`age`:25, `name`:"Tobias"}) create (_1 {`age`:34, `name`:"Peter"}) create (_2:`Swedish` {`age`:36, `belt`:"white", `name`:"Andres"}) create _2-[:`KNOWS`]->_1 create _2-[:`KNOWS`]->_0 match (n) where n:Swedish return n

Filter on node property

To filter on a property, write your clause after the WHERE keyword. Filtering on relationship properties works just the same way.

Query. 

MATCH (n)
WHERE n.age < 30
RETURN n

The "Tobias" node will be returned.

Result

n
1 row

Node[0]{name:"Tobias",age:25}

Try this query live. create (_0 {`age`:25, `name`:"Tobias"}) create (_1 {`age`:34, `name`:"Peter"}) create (_2:`Swedish` {`age`:36, `belt`:"white", `name`:"Andres"}) create _2-[:`KNOWS`]->_1 create _2-[:`KNOWS`]->_0 match (n) where n.age < 30 return n

Property exists

To only include nodes/relationships that have a property, use the HAS() function and just write out the identifier and the property you expect it to have.

Query. 

MATCH (n)
WHERE HAS (n.belt)
RETURN n

The node named "Andres" is returned.

Result

n
1 row

Node[2]{name:"Andres",age:36,belt:"white"}

Try this query live. create (_0 {`age`:25, `name`:"Tobias"}) create (_1 {`age`:34, `name`:"Peter"}) create (_2:`Swedish` {`age`:36, `belt`:"white", `name`:"Andres"}) create _2-[:`KNOWS`]->_1 create _2-[:`KNOWS`]->_0 match (n) where has(n.belt) return n

Regular expressions

Regular expressions

You can match on regular expressions by using =~ "regexp", like this:

Query. 

MATCH (n)
WHERE n.name =~ 'Tob.*'
RETURN n

The "Tobias" node will be returned.

Result

n
1 row

Node[0]{name:"Tobias",age:25}

Try this query live. create (_0 {`age`:25, `name`:"Tobias"}) create (_1 {`age`:34, `name`:"Peter"}) create (_2:`Swedish` {`age`:36, `belt`:"white", `name`:"Andres"}) create _2-[:`KNOWS`]->_1 create _2-[:`KNOWS`]->_0 match (n) where n.name =~ 'Tob.*' return n

Escaping in regular expressions

If you need a forward slash inside of your regular expression, escape it. Remember that back slash needs to be escaped in string literals

Query. 

MATCH (n)
WHERE n.name =~ 'Some\/thing'
RETURN n

No nodes match this regular expression.

Result

n
0 row

(empty result)

Try this query live. create (_0 {`age`:25, `name`:"Tobias"}) create (_1 {`age`:34, `name`:"Peter"}) create (_2:`Swedish` {`age`:36, `belt`:"white", `name`:"Andres"}) create _2-[:`KNOWS`]->_1 create _2-[:`KNOWS`]->_0 match (n) where n.name =~ 'Some\\/thing' return n

Case insensitive regular expressions

By pre-pending a regular expression with (?i), the whole expression becomes case insensitive.

Query. 

MATCH (n)
WHERE n.name =~ '(?i)ANDR.*'
RETURN n

The node with name "Andres" is returned.

Result

n
1 row

Node[2]{name:"Andres",age:36,belt:"white"}

Try this query live. create (_0 {`age`:25, `name`:"Tobias"}) create (_1 {`age`:34, `name`:"Peter"}) create (_2:`Swedish` {`age`:36, `belt`:"white", `name`:"Andres"}) create _2-[:`KNOWS`]->_1 create _2-[:`KNOWS`]->_0 match (n) where n.name =~ '(?i)ANDR.*' return n

Using patterns in WHERE

Filter on patterns

Patterns are expressions in Cypher, expressions that return a collection of paths. Collection expressions are also predicates — an empty collection represents false, and a non-empty represents true.

So, patterns are not only expressions, they are also predicates. The only limitation to your pattern is that you must be able to express it in a single path. You can not use commas between multiple paths like you do in MATCH. You can achieve the same effect by combining multiple patterns with AND.

Note that you can not introduce new identifiers here. Although it might look very similar to the MATCH patterns, the WHERE clause is all about eliminating matched subgraphs. MATCH (a)-[*]->(b) is very different from WHERE (a)-[*]->(b); the first will produce a subgraph for every path it can find between a and b, and the latter will eliminate any matched subgraphs where a and b do not have a directed relationship chain between them.

Query. 

MATCH (tobias { name: 'Tobias' }),(others)
WHERE others.name IN ['Andres', 'Peter'] AND (tobias)<--(others)
RETURN others

Nodes that have an outgoing relationship to the "Tobias" node are returned.

Result

others
1 row

Node[2]{name:"Andres",age:36,belt:"white"}

Try this query live. create (_0 {`age`:25, `name`:"Tobias"}) create (_1 {`age`:34, `name`:"Peter"}) create (_2:`Swedish` {`age`:36, `belt`:"white", `name`:"Andres"}) create _2-[:`KNOWS`]->_1 create _2-[:`KNOWS`]->_0 match (tobias {name: 'Tobias'}), (others) where others.name IN ['Andres', 'Peter'] and (tobias)<--(others) return others

Filter on patterns using NOT

The NOT function can be used to exclude a pattern.

Query. 

MATCH (persons),(peter { name: 'Peter' })
WHERE NOT (persons)-->(peter)
RETURN persons

Nodes that do not have an outgoing relationship to the "Peter" node are returned.

Result

persons
2 rows

Node[0]{name:"Tobias",age:25}

Node[1]{name:"Peter",age:34}

Try this query live. create (_0 {`age`:25, `name`:"Tobias"}) create (_1 {`age`:34, `name`:"Peter"}) create (_2:`Swedish` {`age`:36, `belt`:"white", `name`:"Andres"}) create _2-[:`KNOWS`]->_1 create _2-[:`KNOWS`]->_0 MATCH (persons), (peter {name: 'Peter'}) where not (persons)-->(peter) return persons

Filter on patterns with properties

You can also add properties to your patterns:

Query. 

MATCH (n)
WHERE (n)-[:KNOWS]-({ name:'Tobias' })
RETURN n

Finds all nodes that have a KNOWS relationship to a node with the name Tobias.

Result

n
1 row

Node[2]{name:"Andres",age:36,belt:"white"}

Try this query live. create (_0 {`age`:25, `name`:"Tobias"}) create (_1 {`age`:34, `name`:"Peter"}) create (_2:`Swedish` {`age`:36, `belt`:"white", `name`:"Andres"}) create _2-[:`KNOWS`]->_1 create _2-[:`KNOWS`]->_0 match (n) where (n)-[:KNOWS]-({name:'Tobias'}) return n

Filtering on relationship type

You can put the exact relationship type in the MATCH pattern, but sometimes you want to be able to do more advanced filtering on the type. You can use the special property TYPE to compare the type with something else. In this example, the query does a regular expression comparison with the name of the relationship type.

Query. 

MATCH (n)-[r]->()
WHERE n.name='Andres' AND type(r)=~ 'K.*'
RETURN r

This returns relationships that has a type whose name starts with K.

Result

r
2 rows

:KNOWS[1]{}

:KNOWS[0]{}

Try this query live. create (_0 {`age`:25, `name`:"Tobias"}) create (_1 {`age`:34, `name`:"Peter"}) create (_2:`Swedish` {`age`:36, `belt`:"white", `name`:"Andres"}) create _2-[:`KNOWS`]->_1 create _2-[:`KNOWS`]->_0 match (n)-[r]->() where n.name='Andres' and type(r) =~ 'K.*' return r

Collections

IN operator

To check if an element exists in a collection, you can use the IN operator.

Query. 

MATCH (a)
WHERE a.name IN ["Peter", "Tobias"]
RETURN a

This query shows how to check if a property exists in a literal collection.

Result

a
2 rows

Node[0]{name:"Tobias",age:25}

Node[1]{name:"Peter",age:34}

Try this query live. create (_0 {`age`:25, `name`:"Tobias"}) create (_1 {`age`:34, `name`:"Peter"}) create (_2:`Swedish` {`age`:36, `belt`:"white", `name`:"Andres"}) create _2-[:`KNOWS`]->_1 create _2-[:`KNOWS`]->_0 match (a) where a.name IN ["Peter", "Tobias"] return a

Missing properties and values

Default to false if property is missing

As missing properties evaluate to NULL, the comparision in the example will evaluate to FALSE for nodes without the belt property.

Query. 

MATCH (n)
WHERE n.belt = 'white'
RETURN n

Only nodes with the belt property are returned.

Result

n
1 row

Node[2]{name:"Andres",age:36,belt:"white"}

Try this query live. create (_0 {`age`:25, `name`:"Tobias"}) create (_1 {`age`:34, `name`:"Peter"}) create (_2:`Swedish` {`age`:36, `belt`:"white", `name`:"Andres"}) create _2-[:`KNOWS`]->_1 create _2-[:`KNOWS`]->_0 match (n) where n.belt = 'white' return n

Default to true if property is missing

If you want to compare a property on a graph element, but only if it exists, you can compare the property against both the value you are looking for and NULL, like:

Query. 

MATCH (n)
WHERE n.belt = 'white' OR n.belt IS NULL RETURN n
ORDER BY n.name

This returns all nodes, even those without the belt property.

Result

n
3 rows

Node[2]{name:"Andres",age:36,belt:"white"}

Node[1]{name:"Peter",age:34}

Node[0]{name:"Tobias",age:25}

Try this query live. create (_0 {`age`:25, `name`:"Tobias"}) create (_1 {`age`:34, `name`:"Peter"}) create (_2:`Swedish` {`age`:36, `belt`:"white", `name`:"Andres"}) create _2-[:`KNOWS`]->_1 create _2-[:`KNOWS`]->_0 match (n) where n.belt = 'white' or n.belt IS NULL return n order by n.name

Filter on NULL

Sometimes you might want to test if a value or an identifier is NULL. This is done just like SQL does it, with IS NULL. Also like SQL, the negative is IS NOT NULL, although NOT(IS NULL x) also works.

Query. 

MATCH (person)
WHERE person.name = 'Peter' AND person.belt IS NULL RETURN person

Nodes that have name Peter but no belt property are returned.

Result

person
1 row

Node[1]{name:"Peter",age:34}

Try this query live. create (_0 {`age`:25, `name`:"Tobias"}) create (_1 {`age`:34, `name`:"Peter"}) create (_2:`Swedish` {`age`:36, `belt`:"white", `name`:"Andres"}) create _2-[:`KNOWS`]->_1 create _2-[:`KNOWS`]->_0 match (person) where person.name = 'Peter' AND person.belt is null return person