Quantified path patterns

Path patterns can be used along with quantifiers. The variables within a quantified path can bind to a list of elements instead of a single element.

Quantifier	Description
+	1 or more repetitions.
*	0 or more repetitions.
?	0 or 1 repetitions.
{m,n}	Between m and n repetitions.
{m}	Exactly m repetitions.
{m,}	m or more repetitions.
{,n}	Between 0 and n repetitions.

A path pattern with a quantifier must have a minimum path length greater than 0. The path length is computed as follows:

• The minimum path length of a node n is 0.

• The minimum path length of an edge e is 1.

• The minimum path length of a concatenation of the path patterns p1 and p2 is the sum of their minimum path lengths.

• The minimum path length of an union between the path patterns p1 and p2 is the minimum of minimum path lengths between p1 and p2

For example, the path length of (a)-[e]->(b)-[f]->(c) is 2, since it is the concatenation of 3 node patterns and 2 edge patterns. The rule of the minimum length prevents us to write queries like this:

MATCH p = (a)+
RETURN a

Examples

In this example, we search for paths between John and Jane of length between 0 and 4.

MATCH p = ({name:"John"})-[:Follows]->{,4}({name:"Jane"})
RETURN p

We can use union operators as well. For example, we use the union to combine the results of directed edges and undirected edges.

MATCH p = ({name:"John"})(->|~){2,5}({name:"Jane"})
RETURN p

Unbounded repetition

When using repetition on patterns, the number of results may infinite if the repetition is unbounded. A pattern has unbounded repetition if its quantifier is *, + or {n,}. For example, we search for paths of length at least 1.

MATCH p = ({name:"John"})-[:Follows]->+({name:"Jane"})
RETURN p

To guarantee that the number of results is finite, the statement containing a pattern with unbounded repetition must specify a path mode, a path search prefix or the keyword DIFFERENT EDGES to restrict the result. In the next section, we will see path prefixes.