Introduction
PGQL is a graph patternmatching query language for the property graph data model. This document specifies the syntax and semantics of the language.
Changelog
The following are the changes since PGQL 1.1:
New features since PGQL 1.1
The new features in PGQL 1.2 are:
 Shortest path finding and Topk shortest path finding.
 Scalar subqueries.
 ARRAY_AGG aggregation.
 ABS, CEIL/CEILING, FLOOR and ROUND math functions.
 EXTRACT function for extracting the
year
/month
/day
/hour
/minute
/second
/timezone_hour
/timezone_minute
from datetime values.  CASE statement.
 IN and NOT IN predicates.
Syntax changes since PGQL 1.1
PGQL 1.2 is a superset of PGQL 1.1. There are no changes to existing syntax other than additions.
A note on the Grammar
This document contains a complete grammar definition of PGQL, spread throughout the different sections. There is a single entry point into the grammar: Query
.
Document Outline
 Introduction contains a changelog, a note on the grammar, and this outline.
 Graph Pattern Matching introduces the basic concepts of graph querying.
 Grouping and Aggregation describes the mechanism to group and aggregate results.
 Sorting and Row Limiting describes the ability to sort and paginate results.
 VariableLength Paths introduces the constructs for testing for the existence of paths between pairs of vertices (i.e. “reachability testing”) as well as for retrieving shortest paths between pairs of vertices.
 Functions and Expressions describes the supported data types and corresponding functions and operations.
 Subqueries describes the syntax and semantics of subqueries for creating more complex queries that nest other queries.
 Other Syntactic rules describes additional syntactic rules that are not covered by the other sections, such as syntax for identifiers and comments.
Graph Pattern Matching
Property graph data model
A property graph has a name, which is a (character) string, and contains:

A set of vertices (or nodes).
 Each vertex has zero or more labels.
 Each vertex has zero or more properties (or attributes), which are arbitrary keyvalue pairs.

A set of edges (or relationships).
 Each edge is directed.
 Each edge has zero or more labels.
 Each edge has zero or more properties (or attributes), which are arbitrary keyvalue pairs.
Labels as well as names of properties are strings. Property values are scalars such as numerics, strings or booleans.
Example 1: Student Network
An example graph is:
Here, student_network
is the name of the graph. The graph has three vertices labeled Person
and one vertex labeled University
. There are six directed edges that connect the vertices. Three of them go from person to person vertices, and they have the label knows
. Three others go from person to university vertices and are labeled studentOf
. The person vertices have two properties, namely name
for encoding the name of the person and dob
for encoding the date of birth of the person. The university vertex has only a single property name
for encoding the name of the university. The edges have no properties.
Example 2: Financial Transactions
An example graph with financial transactions is:
Here, financial_transactions
is the name of the graph. The graph has three types of vertices. Vertices labeled Person
or Company
have a property name
, while vertices labeled Account
have a property number
. There are edges labeled ownerOf
from persons to accounts and from companies to accounts, and there are edges labeled transaction
from accounts to accounts. Note that only the transaction edges have a property (amount
).
Writing simple queries
This section is mostly examplebased and is meant for beginning users.
Vertex patterns
The following query matches all the vertices with the label Person
and retrieves their properties name
and dob
:
SELECT n.name, n.dob
FROM student_network
MATCH (n:Person)
++
 n.name  n.dob 
++
 Riya  19950320 
 Kathrine  19940115 
 Lee  19960129 
++
In the query above:
student_network
is the name of the input graph.(n:Person)
is a vertex pattern in whichn
is a variable name and:Person
a label expression. Variable names like
n
can be freely chosen by the user. The vertices that match the pattern are said to “bind to the variable”.  The label expression
:Person
specifies that we match only vertices that have the labelPerson
. n.name
andn.dob
are property references.n.name
andn.dob
access the propertiesname
anddob
of the vertices that bind ton
, respectively.
The query produces three results, which are returned as a table. The results are unordered.
Edge patterns
Edge patterns take the form of arrows like [e]>
(match an outgoing edge) and <[e]
(match an incoming edge).
For example:
SELECT a.name, b.name
FROM student_network
MATCH (a:Person) [e:knows]> (b:Person)
++
 a.name  b.name 
++
 Kathrine  Riya 
 Kathrine  Lee 
 Lee  Kathrine 
++
In the above query:
[e:knows]>
is an edge pattern in whiche
is a variable name and:knows
a label expression. The arrowhead
>
specifies that the pattern matches edges that are outgoing froma
and incoming tob
.
Label expressions
More complex label expressions are supported through label disjunction. Furthermore, it is possible to omit a label expression.
Label disjunction
The bar operator (
) is a logical OR for specifying that a vertex or edge should match as long as it has either of the specified labels.
For example:
SELECT n.name, n.dob
FROM student_network
MATCH (n:PersonUniversity)
++
 n.name  n.dob 
++
 Riya  19950320 
 Kathrine  19940115 
 Lee  19960129 
 UC Berkeley  <null> 
++
In the query above, (n:PersonUniversity)
matches vertices that have either the label Person
or the label University
. Note that in the result, there is a <null>
value in the last row because the corresponding vertex does not have a property dob
.
Omitting a label expression
Label expressions may be omitted altogether. The vertex or edge pattern will then match any vertex or edge, no matter its labels.
For example:
SELECT n.name, n.dob
FROM student_network
MATCH (n)
++
 n.name  n.dob 
++
 Riya  19950320 
 Kathrine  19940115 
 Lee  19960129 
 UC Berkeley  <null> 
++
Note that the query gives the same results as before since both patterns (n)
and (n:PersonUniversity)
match all the vertices in the example graph.
Filters on property values
TODO
Multiple edge patterns
TODO
Matching the same graph element to different patterns
TODO
Matching edges in any direction
Anydirectional edges match edges in the graph no matter if they are incoming or outgoing.
An example query with two anydirectional edges is:
SELECT *
FROM g MATCH (n) [e1] (m) [e2] (o)
Note that in case there are both incoming and outgoing data edges between two data vertices, there will be separate result bindings for each of the edges.
Anydirectional edges may also be used inside common path expressions:
PATH two_hops AS () [e1] () [e2] ()
SELECT *
FROM g MATCH (n) /:two_hops*/> (m)
The above query will return all pairs of vertices n
and m
that are reachable via a multiple of two edges, each edge being either an incoming or an outgoing edge.
Main query structure
The previous section on writing simple queries provided a basic introduction to graph pattern matching. The rest of this document introduces the different functionalities in more detail.
The following is the syntax of the main query structure:
Details of the different clauses of a query can be found in the following sections:
 Common Path Expressions allow for specifying complex reachability queries.
 The SELECT clause specifies what should be returned.
 The FROM clause specifies the name of the input graph.
 The MATCH clause specifies the graph pattern that is to be matched.
 The WHERE clause specifies filters.
 The GROUP BY clause allows for creating groups of results.
 The HAVING clause allows for filtering entire groups of results.
 The ORDER BY clause allows for sorting of results.
 The LIMIT and OFFSET clauses allow for pagination of results.
SELECT
In a PGQL query, the SELECT clause defines the data entities to be returned in the result. In other words, the select clause defines the columns of the result table.
The following explains the syntactic structure of SELECT clause.
SelectClause ::= 'SELECT' 'DISTINCT'? ExpAsVar ( ',' ExpAsVar )*
 'SELECT' '*'
ExpAsVar ::= ValueExpression ( 'AS' VariableName )?
A SELECT
clause consists of the keyword SELECT
followed by either an optional DISTINCT
modifier and commaseparated sequence of ExpAsVar
(“expression as variable”) elements, or, a special character star *
. An ExpAsVar
consists of:
 A
ValueExpression
.  An optional
VariableName
, specified by appending the keywordAS
and the name of the variable.
Consider the following example:
SELECT n, m, n.age AS age
FROM g MATCH (n:Person) [e:friend_of]> (m:Person)
Per each matched subgraph, the query returns two vertices n
and m
and the value for property age of vertex n
. Note that edge e
is omitted from the result even though it is used for describing the pattern.
The DISTINCT
modifier allows for filtering out duplicate results. The operation applies to an entire result row, such that rows are only considered duplicates of each other if they contain the same set of values.
Assigning variable name to Select Expression
It is possible to assign a variable name to any of the selection expression, by appending the keyword AS
and a variable name. The variable name is used as the column name of the result set. In addition, the variable name can be later used in the ORDER BY
clause. See the related section later in this document.
SELECT n.age * 2  1 AS pivot, n.name, n
FROM g MATCH (n:Person) > (m:Car)
ORDER BY pivot
SELECT *
SELECT *
is a special SELECT
clause. The semantic of SELECT *
is to select all the variables in the graph pattern.
Consider the following query:
SELECT *
FROM g MATCH (n:Person) > (m) > (w)
, (n) > (w) > (m)
This query is semantically equivalent to:
SELECT n, m, w
FROM g MATCH (n:Person) > (m) > ()
, (n) > (w) > (m)
SELECT *
is not allowed when the graph pattern has zero variables. This is the case when all the vertices and edges in the pattern are anonymous (e.g. MATCH () > (:Person)
).
Futhermore, SELECT *
in combination with GROUP BY
is not allowed.
FROM
The FROM
clause specifies the name of the input graph to be queried:
FromClause ::= 'FROM' GraphName
GraphName ::= IDENTIFIER
For example, the input graph of the following query is my_graph
:
SELECT p.first_name, p.last_name
FROM my_graph
MATCH (p:Person)
ORDER BY p.first_name, p.last_name
Default graphs
The FROM
clause may be omitted if there is a “default graph” such that specifying the graph name inside the query is only redundant.
PGQL itself does not (yet) provide syntax for specifying a default graph. However, PGQL engines like PGX provide APIs like PgxGraph.queryPgql(..)
that provide a default graph (whose name corresponds to PgxGraph.getName()
). This in contrast to APIs like PgxSession.queryPgql(..)
which do not provide default graphs.
If a default graph is provided then the FROM
clause can be omitted from a query like in this example:
SELECT p.first_name, p.last_name
MATCH (p:Person)
ORDER BY p.first_name, p.last_name
MATCH
In a PGQL query, the MATCH
clause defines the graph pattern to be matched.
Syntactically, a MATCH
clause is composed of the keyword MATCH
followed by a commaseparated sequence of path patterns:
MatchClause ::= 'MATCH' GraphPattern
GraphPattern ::= PathPattern ( ',' PathPattern )*
PathPattern ::= SimplePathPattern
 ShortestPathPattern
 TopKShortestPathPattern
SimplePathPattern ::= VertexPattern ( PathPrimary VertexPattern )*
VertexPattern ::= '(' VariableSpecification ')'
PathPrimary ::= EdgePattern
 ReachabilityPathExpression
EdgePattern ::= OutgoingEdgePattern
 IncomingEdgePattern
 AnyDirectionalEdgePattern
OutgoingEdgePattern ::= '>'
 '[' VariableSpecification ']>'
IncomingEdgePattern ::= '<'
 '<[' VariableSpecification ']'
AnyDirectionalEdgePattern ::= ''
 '[' VariableSpecification ']'
VariableSpecification ::= VariableName? LabelPredicate?
VariableName ::= IDENTIFIER
A path pattern that describes a partial topology of the subgraph pattern. In other words, a topology constraint describes some connectivity relationships between vertices and edges in the pattern, whereas the whole topology of the pattern is described with one or multiple topology constraints.
A topology constraint is composed of one or more vertices and relations, where a relation is either an edge or a path. In a query, each vertex or edge is (optionally) associated with a variable, which is a symbolic name to reference the vertex or edge in other clauses. For example, consider the following topology constraint:
(n) [e]> (m)
The above example defines two vertices (with variable names n
and m
), and an edge (with variable name e
) between them. Also the edge is directed such that the edge e
is an outgoing edge from vertex n
.
More specifically, a vertex term is written as a variable name inside a pair of parenthesis ()
. An edge term is written as a variable name inside a square bracket []
with two dashes and an inequality symbol attached to it – which makes it look like an arrow drawn in ASCII art. An edge term is always connected with two vertex terms as for the source and destination vertex of the edge; the source vertex is located at the tail of the ASCII arrow and the destination at the head of the ASCII arrow.
There can be multiple path patterns in the MATCH
clause of a PGQL query. Semantically, all constraints are conjunctive – that is, each matched result should satisfy every constraint in the MATCH
clause.
Repeated variables
There can be multiple topology constraints in the WHERE
clause of a PGQL query. In such a case, vertex terms that have the same variable name correspond to the same vertex entity. For example, consider the following two lines of topology constraints:
(n) [e1]> (m1),
(n) [e2]> (m2)
Here, the vertex term (n)
in the first constraint indeed refers to the same vertex as the vertex term (n)
in the second constraint. It is an error, however, if two edge terms have the same variable name, or, if the same variable name is assigned to an edge term as well as to a vertex term in a single query.
Alternatives for specifying graph patterns
There are various ways in which a particular graph pattern can be specified.
First, a single path pattern can be written as a chain of edge terms such that two consecutive edge terms share the common vertex term in between. For example:
(n1) [e1]> (n2) [e2]> (n3) [e3]> (n4)
The above graph pattern is equivalent to the graph pattern specified by the following set of commaseparate path patterns:
(n1) [e1]> (n2),
(n2) [e2]> (n3),
(n3) [e3]> (n4)
Second, it is allowed to reverse the direction of an edge in the pattern, i.e. righttoleft instead of lefttoright. Therefore, the following is a valid graph pattern:
(n1) [e1]> (n2) <[e2] (n3)
Please mind the edge directions in the above query – vertex n2
is a common outgoing neighbor of both vertex n1
and vertex n3
.
Third, it is allowed to ommitg variable names if the particular vertex or edge does not need to be referenced in any of the other clauses (e.g. SELECT
or ORDER BY
). When the variable name is omitted, the vertex or edge is an “anonymous” vertex or edge.
Syntactically, for vertices, this result in an empty pair of parenthesis. In case of edges, the whole square bracket is omitted in addition to the variable name.
The following table summarizes these short cuts.
Syntax form  Example 

Basic form  (n) [e]> (m) 
Omit variable name of the source vertex  () [e]> (m) 
Omit variable name of the destination vertex  (n) [e]> () 
Omit variable names in both vertices  () [e]> () 
Omit variable name in edge  (n) > (m) 
Disconnected graph patterns
In the case the MATCH
clause contains two or more disconnected graph patterns (i.e. groups of vertices and relations that are not connected to each other), the different groups are matched independently and the final result is produced by taking the Cartesian product of the result sets of the different groups. The following is an example:
SELECT *
FROM g MATCH (n1) > (m1), (n2) > (m2)
Here, vertices n2
and m2
are not connected to vertices n1
and m1
, resulting in a Cartesian product.
Label predicates
In the property graph model, vertices and edge may have labels, which are arbitrary (character) strings. Typically, labels are used to encode types of entities. For example, a graph may contain a set of vertices with the label Person
, a set of vertices with the label Movie
, and, a set of edges with the label likes
. A label predicate specifies that a vertex or edge only matches if it has ony of the specified labels. The syntax for specifying a label predicate is through a (:
) followed by one or more labels that are separate by a vertical bar (
).
This is explained by the following grammar constructs:
LabelPredicate ::= ':' Label ( '' Label )*
Label ::= IDENTIFIER
Take the following example:
SELECT *
FROM g MATCH (x:Person) [e:likesknows]> (y:Person)
Here, we specify that vertices x
and y
have the label Person
and that the edge e
has the label likes
or the label knows
.
A label predicate can be specified even when a variable is omitted. For example:
SELECT *
FROM g MATCH (:Person) [:likesknows]> (:Person)
There are also builtin functions available for labels (see Builtin Functions):
has_label(element, string)
returnstrue
if the vertex or edge (first argument) has the specified label (second argument).labels(element)
returns the set of labels of a vertex or edge in the case the vertex/edge has multiple labels.label(element)
returns the label of a vertex or edge in the case the vertex/edge has only a single label.
WHERE
Filters are applied after pattern matching to remove certain solutions. A filter takes the form of a boolean value expression which typically involves certain property values of the vertices and edges in the graph pattern.
The syntax is:
WhereClause ::= 'WHERE' ValueExpression
For example:
SELECT y.name
FROM g MATCH (x) > (y)
WHERE x.name = 'Jake'
AND y.age > 25
Here, the first filter describes that the vertex x
has a property name
and its value is Jake
. Similarly, the second filter describes that the vertex y
has a property age
and its value is larger than 25
. Here, in the filter, the dot (.
) operator is used for property access. For the detailed syntax and semantic of expressions, see Functions and Expressions.
Note that the ordering of constraints does not have an affect on the result, such that query from the previous example is equivalent to:
SELECT y.name
FROM g MATCH (x) > (y)
WHERE y.age > 25
AND x.name = 'Jake'
Grouping and Aggregation
GROUP BY
GROUP BY
allows for grouping of solutions and is typically used in combination with aggregates like MIN
and MAX
to compute aggregations over groups of solutions.
The following explains the syntactic structure of the GROUP BY
clause:
GroupByClause ::= 'GROUP' 'BY' ValueExpression ( ',' ValueExpression )*
The GROUP BY
clause starts with the keywords GROUP BY and is followed by a commaseparated list of value expressions that can be of any type.
Consider the following query:
SELECT n.first_name, COUNT(*), AVG(n.age)
FROM g MATCH (n:Person)
GROUP BY n.first_name
Matches are grouped by their values for n.first_name
. For each group, the query selects n.first_name
(i.e. the group key), the number of solutions in the group (i.e. COUNT(*)
), and the average value of the property age for vertex n (i.e. AVG(n.age)
).
Multiple Terms in GROUP BY
It is possible that the GROUP BY
clause consists of multiple terms. In such a case, matches are grouped together only if they hold the same result for each of the group expressions.
Consider the following query:
SELECT n.first_name, n.last_name, COUNT(*)
FROM g MATCH (n:Person)
GROUP BY n.first_name, n.last_name
Matches will be grouped together only if they hold the same values for n.first_name
and the same values for n.last_name
.
GROUP BY and NULL values
The group for which all the group keys are null is a valid group and takes part in further query processing.
To filter out such a group, use a HAVING
clause (see HAVING), for example:
SELECT n.prop1, n.prop2, COUNT(*)
FROM g MATCH (n)
GROUP BY n.prop1, n.prop2
HAVING n.prop1 IS NOT NULL AND n.prop2 IS NOT NULL
Repetition of Group Expression in Select or Order Expression
Group expressions may be repeated in select or order expressions.
Consider the following query:
SELECT n.age, COUNT(*)
FROM g MATCH (n)
GROUP BY n.age
ORDER BY n.age
Here, the group expression n.age
is repeated in the SELECT and ORDER BY.
Aggregation
Aggregates COUNT
, MIN
, MAX
, AVG
and SUM
can aggregate over groups of solutions.
The syntax is:
Aggregation ::= CountAggregation
 MinAggregation
 MaxAggregation
 AvgAggregation
 SumAggregation
 ArrayAggregation
CountAggregation ::= 'COUNT' '(' '*' ')'
 'COUNT' '(' 'DISTINCT'? ValueExpression ')'
MinAggregation ::= 'MIN' '(' 'DISTINCT'? ValueExpression ')'
MaxAggregation ::= 'MAX' '(' 'DISTINCT'? ValueExpression ')'
AvgAggregation ::= 'AVG' '(' 'DISTINCT'? ValueExpression ')'
SumAggregation ::= 'SUM' '(' 'DISTINCT'? ValueExpression ')'
ArrayAggregation ::= 'ARRAY_AGG' '(' 'DISTINCT'? ValueExpression ')'
Syntactically, an aggregation takes the form of aggregate followed by an optional DISTINCT
modifier and a ValueExpression
.
The following table gives an overview of the different aggregates and their supported input types.
Aggregate Operator  Semantic  Required Input Type 

COUNT 
counts the number of times the given expression has a bound (i.e. is not null).  any type, including vertex and edge 
MIN 
takes the minimum of the values for the given expression.  numeric, string, boolean, date, time [with time zone], or, timestamp [with time zone] 
MAX 
takes the maximum of the values for the given expression.  numeric, string, boolean, date, time [with time zone], or, timestamp [with time zone] 
SUM 
sums over the values for the given expression.  numeric 
AVG 
takes the average of the values for the given expression.  numeric 
ARRAY_AGG 
constructs an array/list of the values for the given expression.  numeric, string, boolean, date, time [with time zone], or, timestamp [with time zone] 
Aggregation with GROUP BY
If a GROUP BY
is specified, aggregations are applied to each individual group of solutions.
For example:
SELECT AVG(m.salary)
FROM g MATCH (m:Person)
GROUP BY m.age
Here, we group people by their age and compute the average salary for each such a group.
Aggregation without GROUP BY
If no GROUP BY
is specified, aggregations are applied to the entire set of solutions.
For example:
SELECT AVG(m.salary)
FROM g MATCH (m:Person)
Here, we aggregate over the entire set of vertices with label Person
, to compute the average salary.
COUNT(*)
COUNT(*)
is a special construct that simply counts the number of solutions without evaluating an expression.
For example:
SELECT COUNT(*)
FROM g MATCH (m:Person)
DISTINCT in aggregation
The DISTINCT
modifier specifies that duplicate values should be removed before performing aggregation.
For example:
SELECT AVG(DISTINCT m.age)
FROM g MATCH (m:Person)
Here, we aggregate only over distinct m.age
values.
HAVING
The HAVING
clause is an optional clause that can be placed after a GROUP BY
clause to filter out particular groups of solutions.
The syntax is:
HavingClause ::= 'HAVING' ValueExpression
For example:
SELECT n.name
FROM g MATCH (n) [:has_friend]> (m)
GROUP BY n
HAVING COUNT(m) > 10
This query returns the names of people who have more than 10 friends.
Sorting and Row Limiting
ORDER BY
When there are multiple matched subgraph instances to a given query, in general, the ordering between those instances are not defined; the query execution engine can present the result in any order. Still, the user can specify the ordering between the answers in the result using ORDER BY
clause.
The following explains the syntactic structure of ORDER BY
clause.
OrderByClause ::= 'ORDER' 'BY' OrderTerm ( ',' OrderTerm )*
OrderTerm ::= ValueExpression ( 'ASC'  'DESC' )?
The ORDER BY
clause starts with the keywords ORDER BY
and is followed by comma separated list of order terms. An order term consists of the following parts:
 An expression.
 An optional ASC or DESC decoration to specify that ordering should be ascending or descending.
 If no keyword is given, the default is ascending order.
The following is an example in which the results are ordered by property access n.age
in ascending order:
SELECT n.name
FROM g MATCH (n:Person)
ORDER BY n.age ASC
Data types for ORDER BY
A partial ordering for the different data types is defined as follows:
 Numeric values are ordered from small to large.
 String values are ordered lexicographically.
 Boolean values are ordered such that
false
comes beforetrue
.  Datetime values (i.e. dates, times, or timestamps) are ordered such that earlier points in time come before later points in time.
Vertices and edges cannot be ordered directly.
Multiple expressions in ORDER BY
An ORDER BY
may contain more than one expression, in which case the expresisons are evaluated from left to right. That is, (n+1)th ordering term is used only for the tiebreak rule for nth ordering term. Note that different expressions can have different ascending or descending decorators.
SELECT f.name
FROM g MATCH (f:Person)
ORDER BY f.age ASC, f.salary DESC
LIMIT and OFFSET
The LIMIT
puts an upper bound on the number of solutions returned, whereas the OFFSET
specifies the start of the first solution that should be returned.
The following explains the syntactic structure for the LIMIT and OFFSET clauses:
LimitOffsetClauses ::= 'LIMIT' LimitOffsetValue ( 'OFFSET' LimitOffsetValue )?
 'OFFSET' LimitOffsetValue ( 'LIMIT' LimitOffsetValue )?
LimitOffsetValue ::= UNSIGNED_INTEGER
 BindVariable
The LIMIT
clause starts with the keyword LIMIT
and is followed by an integer that defines the limit. Similarly, the OFFSET
clause starts with the keyword OFFSET
and is followed by an integer that defines the offset. Furthermore:
The LIMIT
and OFFSET
clauses can be defined in either order.
The limit and offset may not be negatives.
The following semantics hold for the LIMIT
and OFFSET
clauses:
The OFFSET
clause is always applied first, even if the LIMIT
clause is placed before the OFFSET
clause inside the query.
An OFFSET
of zero has no effect and gives the same result as if the OFFSET
clause was omitted.
If the number of actual solutions after OFFSET
is applied is greater than the limit, then at most the limit number of solutions will be returned.
In the following query, the first 5 intermediate solutions are pruned from the result (i.e. OFFSET 5
). The next 10 intermediate solutions are returned and become final solutions of the query (i.e. LIMIT 10
).
SELECT n
FROM g MATCH (n)
LIMIT 10
OFFSET 5
VariableLength Paths
Path queries test for the existence of arbitrarylength paths between pairs of vertices, or, retrieve actual paths between pairs of vertices.
Quantifiers
Quantifiers in path patterns allow for specifying lower and upper limits on the number of times a pattern should match.
The syntax is:
GraphPatternQuantifier ::= ZeroOrMore
 OneOrMore
 Optional
 ExactlyN
 NOrMore
 BetweenNAndM
 BetweenZeroAndM
ZeroOrMore ::= '*'
OneOrMore ::= '+'
Optional ::= '?'
ExactlyN ::= '{' UNSIGNED_INTEGER '}'
NOrMore ::= '{' UNSIGNED_INTEGER ',' '}'
BetweenNAndM ::= '{' UNSIGNED_INTEGER ',' UNSIGNED_INTEGER '}'
BetweenZeroAndM ::= '{' ',' UNSIGNED_INTEGER '}'
The meaning of the different quantifiers is:
quantifier  meaning  matches  example path 

*  zero (0) or more  A path that connects the source and destination of the path by zero or more matches of a given pattern.  /:lbl*/> 
+  one (1) or more  A path that connects the source and destination of the path by one or more matches of a given pattern.  /:lbl+/> 
?  zero or one (1), i.e. “optional”  A path that connects the source and destination of the path by zero or one matches of a given pattern.  /:lbl?/> 
{ n }  exactly n  A path that connects the source and destination of the path by exactly n matches of a given pattern.  /:lbl{2}/> 
{ n, }  n or more  A path that connects the source and destination of the path by at least n matches of a given pattern.  /:lbl{2,}/> 
{ n, m }  between n and m (inclusive)  A path that connects the source and destination of the path by at least n and at most m (inclusive) matches of a given pattern.  /:lbl{2,3}/> 
{ , m }  between zero (0) and m (inclusive)  A path that connects the source and destination of the path by at least 0 and at most m (inclusive) matches of a given pattern.  /:lbl{,3}/> 
Paths considered include those that repeat the same vertices and/or edges multiple times. This means that even cycles are considered.
Reachability
In graph reachability we test for the existence of paths (true/false) between pairs of vertices. PGQL uses forward slashes (/
and />
) instead of square brackets ([
and ]>
) to indicate reachability semantic.
The syntax is:
ReachabilityPathExpression ::= OutgoingPathPattern
 IncomingPathPattern
OutgoingPathPattern ::= '/' PathSpecification '/>'
IncomingPathPattern ::= '</' PathSpecification '/'
PathSpecification ::= LabelPredicate
 PathPredicate
PathPredicate ::= ':' Label GraphPatternQuantifier?
For example:
SELECT c.name
FROM g MATCH (c:Class) /:subclass_of*/> (arrayList:Class)
WHERE arrayList.name = 'ArrayList'
Here, we find all classes that are a subclass of 'ArrayList'
. The regular path pattern subclass_of*
matches a path consisting of zero or more edges with the label subclass_of
. Because the pattern may match a path with zero edges, the two query vertices can be bound to the same data vertex if the data vertex satisfies the constraints specified in both source and destination vertices (i.e. the vertex has a label Class
and a property name
with a value ArrayList
).
Examples with various quantifiers
Zero or more
The following example finds all vertices y
that can be reached from Amy
by following zero or more likes
edges.
SELECT y.name
FROM g MATCH (x:Person) /:likes*/> (y)
WHERE x.name = 'Amy'
++
 y.name 
++
 Amy 
 John 
 Albert 
 Judith 
++
Note that here, Amy
is returned since Amy
connects to Amy
by following zero likes
edges. In other words, there exists an empty path for the vertex pair.
For Judith
, there exist two paths (100 > 200 > 300 > 400
and 100 > 400
). However, Judith
is still only returned once since the semantic of / .. />
is to test for the existence of paths between pairs of vertices (i.e. “reachability”), so there is only at most one result per pair of vertices.
One or more
The following example finds all people that can be reached from Amy
by following one or more likes
edges.
SELECT y.name
FROM g MATCH (x:Person) /:likes+/> (y)
WHERE x.name = 'Amy'
++
 y.name 
++
 John 
 Albert 
 Judith 
++
This time, Amy
is not returned since there does not exist a path that connects Amy
to Amy
that has a length greater than zero.
The following example finds all people that can be reached from Judith
by following one or more knows
edges:
SELECT y.name
FROM g MATCH (x:Person) /:knows+/> (y)
WHERE x.name = 'Judith'
++
 y.name 
++
 Jonas 
 Judith 
++
Here, in addition to Jonas
, Judith
is returned since there exist paths from Judith
back to Judith
that has a length greater than zero. Examples of such paths are 400 > 500 > 400
and 400 > 500 > 400 > 500 > 400
.
Optional
The following example finds all people that can be reached from Judith
by following zero or one knows
edges.
SELECT y.name
FROM g MATCH (x:Person) /:knows?/> (y)
WHERE x.name = 'Judith'
++
 y.name 
++
 Judith 
 Jonas 
++
Here, Judith
is returned since there exists the empty path that starts in 400
and ends in 400
. Jonas
is returned because of the following path that has length one: 400 > 500
.
Exactly n
The following example finds all people that can be reached from Amy
by following exactly two likes
edges.
SELECT y.name
FROM g MATCH (x:Person) /:likes{2}/> (y)
WHERE x.name = 'Amy'
++
 y.name 
++
 Albert 
++
Here, Albert
is returned since there exists the following path that has likes
edges only: 100 > 200 > 300
.
n or more
The following example finds all people that can be reached from Amy
by following 2 or more likes
edges.
SELECT y.name
FROM g MATCH (x:Person) /:likes{2,}/> (y)
WHERE x.name = 'Amy'
++
 y.name 
++
 Albert 
 Judith 
++
Here, Albert
is returned since there exists the following path of length two: 100 > 200 > 300
. Judith
is returned since there exists a path of length three: 100 > 200 > 300 > 400
.
Between n and m
The following example finds all people that can be reached from Amy
by following between 1 and 2 likes
edges.
SELECT y.name
FROM g MATCH (x:Person) /:likes{1,2}/> (y)
WHERE x.name = 'Amy'
++
 y.name 
++
 John 
 Albert 
 Judith 
++
Here, John
is returned since there exists a path of length one (i.e. 100 > 200
);
Albert
is returned since there exists a path of length two (i.e. 100 > 200 > 300
);
Judith
is returned since there exists a path of length one (i.e. 100 > 400
).
Between zero and m
The following example finds all people that can be reached from Judith
by following at most 2 knows
edges.
SELECT y.name
FROM g MATCH (x:Person) /:knows{,2}/> (y)
WHERE x.name = 'Judith'
++
 y.name 
++
 Jonas 
 Judith 
++
Here, Jonas
is returned since there exists a path of length one (i.e. 400 > 500
).
For Judith
, there exists an empty path of length zero (i.e. 400
) as well as a nonempty path of length two (i.e. 400 > 500 > 400
).
Yet, Judith
is only returned once.
Common Path Expressions
One or more “common path expression” may be declared at the beginning of the query. These can be seen as macros that allow for expressing complex regular expressions. PGQL 1.2 allows common path expressions only for reachability, not for (topk) shortest path.
CommonPathExpressions ::= CommonPathExpression+
CommonPathExpression ::= 'PATH' IDENTIFIER 'AS' PathPattern WhereClause?
A path pattern declaration starts with the keyword PATH
, followed by an expression name, the assignment operator AS
, and a path pattern consisting of at least one vertex. The syntactic structure of the path pattern is the same as a path pattern in the MATCH
clause.
For example:
PATH has_parent AS () [:has_fatherhas_mother]> (:Person)
SELECT ancestor.name
FROM g MATCH (p1:Person) /:has_parent+/> (ancestor)
, (p2:Person) /:has_parent+/> (ancestor)
WHERE p1.name = 'Mario'
AND p2.name = 'Luigi'
The above query finds common ancestors of Mario
and Luigi
.
Another example is:
PATH connects_to AS (:Generator) [:has_connector]> (c:Connector) <[:has_connector] (:Generator)
WHERE c.status = 'OPERATIONAL'
SELECT generatorA.location, generatorB.location
FROM g MATCH (generatorA) /:connects_to+/> (generatorB)
The above query outputs all generators that are connected to each other via one or more connectors that are all operational.
Shortest Path
SHORTEST
allows for matching a shortest path (i.e. minimal number of edges) between a source vertex and a destination vertex. In case multiple shortest paths exist, an arbitrary one is retrieved.
The syntax is:
ShortestPathPattern ::= 'SHORTEST' '(' SourceVertexPattern
QuantifiedShortestPathPrimary
DestinationVertexPattern ')'
SourceVertexPattern ::= VertexPattern
DestinationVertexPattern ::= VertexPattern
QuantifiedShortestPathPrimary ::= ShortestPathPrimary GraphPatternQuantifier?
ShortestPathPrimary ::= EdgePattern
 ParenthesizedPathPatternExpression
ParenthesizedPathPatternExpression ::= '(' VertexPattern? EdgePattern VertexPattern? WhereClause? ')'
For example:
SELECT src, SUM(e.weight), dst
FROM g
MATCH SHORTEST ( (src) [e]>* (dst) )
WHERE src.age < dst.age
Another example is:
SELECT COUNT(e) AS num_hops
, p1.name AS start
, ARRAY_AGG ( CASE
WHEN has_label(dst, 'Account')
THEN CAST(dst.number AS STRING)
ELSE dst.name
END
) AS path
FROM financial_transactions
MATCH SHORTEST ( (p1:Person) ([e] (dst))* (p2:Person) )
WHERE p1.name = 'Camille' AND p2.name = 'Liam'
ORDER BY num_hops
++
 num_hops  start  path 
++
 3  Camille  [10039, 2090, Liam] 
++
Filters on vertices and edges along paths can be specified by adding a WHERE
clause inside the quantified pattern.
For example, the following query matches a shortest path (if one exists) such that each edge along the path has a property weight
with a value greater than 10
:
SELECT src, ARRAY_AGG(e.weight), dst
FROM g
MATCH SHORTEST ( (src) ([e]> WHERE e.weight > 10)* (dst) )
Note that this is different from a WHERE
clause that is placed outside of the quantified pattern:
SELECT src, ARRAY_AGG(e.weight), dst
FROM g
MATCH SHORTEST ( (src) [e]>* (dst) ) WHERE SUM(e.cost) < 100
Here, the filter is applied only after a shortest path is matched such that if the WHERE
condition is not satisfied, the path is filtered out and no other path is considered even though another path may exist that does satisfy the WHERE
condition.
TopK Shortest Path
TOP
k SHORTEST
path matches the k shortest paths for each pair of source and destination vertices. Aggregations can then be computed over their vertices/edges.
The syntax is:
TopKShortestPathPattern ::= 'TOP' KValue ShortestPathPattern
KValue ::= UNSIGNED_INTEGER
For example the following query will output the sum of the edge weights along each of the top 3 shortest paths between each of the matched source and destination pairs:
SELECT src, SUM(e.weight), dst
FROM g
MATCH TOP 3 SHORTEST ( (src) [e]>* (dst) )
WHERE src.age < dst.age
Notice that the sum aggregation is computed for each matching path. In other words, the number of rows returned by the query is equal to the number of paths that match, which is at most three times the number of possible sourcedestination pairs.
The ARRAY_AGG
construct allows users to output properties of edges/vertices along the path. For example, in the following query:
SELECT src, ARRAY_AGG(e.weight), ARRAY_AGG(v1.age), ARRAY_AGG(v2.age), dst
FROM g
MATCH TOP 3 SHORTEST ( (src) ((v1) [e]> (v2))* (dst) )
WHERE src.age < dst.age
the ARRAY_AGG(e.weight)
outputs a list containing the weight property of all the edges along the path,
the ARRAY_AGG(v1.cost)
outputs a list containing the age property of all the vertices along the path except the last one,
the ARRAY_AGG(v2.cost)
outputs a list containing the age property of all the vertices along the path except the first one.
Users can also compose shortest path constructs with other matching operators:
SELECT ARRAY_AGG(e1.weight), ARRAY_AGG(e2.weight)
FROM g
MATCH (start) > (src)
, TOP 3 SHORTEST ( (src) ([e1]>)* (mid) )
, SHORTEST ( (mid) ([e2]>)* (dst) )
, (dst) > (end)
Another example is:
SELECT COUNT(e) AS num_hops
, SUM(e.amount) AS total_amount
, ARRAY_AGG(e.amount) AS amounts_along_path
FROM financial_transactions
MATCH TOP 7 SHORTEST ( (a:Account) [e:transaction]>* (b:Account) )
WHERE a.number = 10039 AND a = b
ORDER BY num_hops, total_amount
++
 num_hops  total_amount  amounts_along_path 
++
 0  <null>  <null> 
 4  22399.8  [1000.0, 1500.3, 9999.5, 9900.0] 
 4  23900.2  [1000.0, 3000.7, 9999.5, 9900.0] 
 8  44799.6  [1000.0, 1500.3, 9999.5, 9900.0, 1000.0, 1500.3, 9999.5, 9900.0] 
 8  46300.0  [1000.0, 1500.3, 9999.5, 9900.0, 1000.0, 3000.7, 9999.5, 9900.0] 
 8  46300.0  [1000.0, 3000.7, 9999.5, 9900.0, 1000.0, 1500.3, 9999.5, 9900.0] 
 8  47800.4  [1000.0, 3000.7, 9999.5, 9900.0, 1000.0, 3000.7, 9999.5, 9900.0] 
++
Note that above, we matched a path with zero edges (the first result) and we also matched four paths (the last four results) that visit the same edges multiple times. The following example shows how such paths could be filtered out, such that we only keep paths that have at least one edge and that do not visit an edge multiple times:
SELECT COUNT(e) AS num_hops
, SUM(e.amount) AS total_amount
, ARRAY_AGG(e.amount) AS amounts_along_path
FROM financial_transactions
MATCH TOP 7 SHORTEST ( (a:Account) [e:transaction]>* (b:Account) )
WHERE a.number = 10039 AND a = b AND COUNT(DISTINCT e) = COUNT(e) AND COUNT(e) > 0
ORDER BY num_hops, total_amount
++
 num_hops  total_amount  amounts_along_path 
++
 4  22399.8  [1000.0, 1500.3, 9999.5, 9900.0] 
 4  23900.2  [1000.0, 3000.7, 9999.5, 9900.0] 
++
Functions and Expressions
Value expressions are used in various parts of the language, for example, to filter solutions (WHERE
and HAVING
), to project out computed values (SELECT
), or, to group by or order by computed values (GROUP BY
and ORDER BY
).
The following are the relevant grammar rules:
ValueExpression ::= VariableReference
 PropertyAccess
 Literal
 BindVariable
 ArithmeticExpression
 RelationalExpression
 LogicalExpression
 BracketedValueExpression
 FunctionInvocation
 Aggregation
 ExtractFunction
 IsNullPredicate
 IsNotNullPredicate
 CastSpecification
 CaseExpression
 InPredicate
 NotInPredicate
 ExistsPredicate
 ScalarSubquery
VariableReference ::= VariableName
PropertyAccess ::= VariableReference '.' PropertyName
PropertyName ::= IDENTIFIER
BracketedValueExpression ::= '(' ValueExpression ')'
A value expression is one of:
 A variable reference, being either a reference to a
VertexPattern
, anEdgePattern
, or anExpAsVar
.  A property access, which syntactically takes the form of a variable reference, followed by a dot (
.
) and the name of a property.  A literal (see Literals).
 A bind variable (see Bind Variables).
 An arithmetic, relational, or logical expression (see Operators).
 A bracketed value expression, which syntactically takes the form of a value expression between rounded brackets. The brackets allow for controlling precedence.
 A function invocation (see String functions, Numeric functions, Datetime functions and Vertex and Edge functions).
 The
IS NULL
andIS NOT NULL
predicates (see IS NULL and IS NOT NULL).  The
EXISTS
predicate (see EXISTS and NOT EXISTS subqueries).  An aggregation (see Aggregation).
Data Types and Literals
Data Types
PGQL has the following data types:
STRING
NUMERIC
(e.g.INT
/INTEGER
,LONG
,FLOAT
,DOUBLE
)BOOLEAN
DATE
TIME
TIMESTAMP
TIME WITH TIME ZONE
TIMESTAMP WITH TIME ZONE
Literals
The syntax is:
Literal ::= StringLiteral
 NumericLiteral
 BooleanLiteral
 DateLiteral
 TimeLiteral
 TimestampLiteral
 TimeWithTimeZoneLiteral
 TimestampWithTimeZoneLiteral
StringLiteral ::= SINGLE_QUOTED_STRING
NumericLiteral ::= UNSIGNED_INTEGER
 UNSIGNED_DECIMAL
BooleanLiteral ::= 'true'
 'false'
DateLiteral ::= 'DATE' "'" <yyyyMMdd> "'"
TimeLiteral ::= 'TIME' "'" <HH:mm:ss> "'"
TimestampLiteral ::= 'TIMESTAMP' "'" <yyyyMMdd HH:mm:ss> "'"
TimeWithTimeZoneLiteral ::= 'TIME' "'" <HH:mm:ss+HH:MM> "'"
TimestampWithTimeZoneLiteral ::= 'TIMESTAMP' "'" <yyyyMMdd HH:mm:ss+HH:MM> "'"
For example:
Literal type  Example literal 

string  'Clara' 
integer  12 
decimal  12.3 
boolean  true 
date  DATE '20170921' 
time  TIME '16:15:00' 
timestamp  TIMESTAMP '20170921 16:15:00' 
time with time zone  TIME '16:15:00+01:00' 
timestamp with time zone  TIMESTAMP '20170921 16:15:0003:00' 
Note that according to the grammar rules, numeric literals (integer and decimal) are unsigned. However, signed values can be generated by using the unary minus operator (
).
Bind Variables
In place of a literal, one may specify a bind variable (?
). This allows for specifying parameterized queries.
An example query with two bind variables is as follows:
SELECT n.age
FROM g MATCH (n)
WHERE n.name = ?
OR n.age > ?
In the following query, bind variables are used in LIMIT
and OFFSET
:
SELECT n.name, n.age
FROM g MATCH (n)
ORDER BY n.age
LIMIT ?
OFFSET ?
The following example shows a bind variable in the position of a label:
SELECT n.name
FROM g MATCH (n)
WHERE has_label(n, ?)
Operators
Arithmetic, Relational and Logical Operators
The following table is an overview of the operators:
Operator kind  Operator 

Arithmetic  + ,  , * , / , % ,  (unary minus) 
Relational  = , <> , < , > , <= , >= 
Logical  AND , OR , NOT 
The corresponding grammar rules are:
ArithmeticExpression ::= UnaryMinus
 Multiplication
 Division
 Modulo
 Addition
 Subtraction
UnaryMinus ::= '' ValueExpression
Multiplication ::= ValueExpression '*' ValueExpression
Division ::= ValueExpression '/' ValueExpression
Modulo ::= ValueExpression '%' ValueExpression
Addition ::= ValueExpression '+' ValueExpression
Subtraction ::= ValueExpression '' ValueExpression
RelationalExpression ::= Equal
 NotEqual
 Greater
 Less
 GreaterOrEqual
 LessOrEqual
Equal ::= ValueExpression '=' ValueExpression
NotEqual ::= ValueExpression '<>' ValueExpression
Greater ::= ValueExpression '>' ValueExpression
Less ::= ValueExpression '<' ValueExpression
GreaterOrEqual ::= ValueExpression '>=' ValueExpression
LessOrEqual ::= ValueExpression '<=' ValueExpression
LogicalExpression ::= Not
 And
 Or
Not ::= 'NOT' ValueExpression
And ::= ValueExpression 'AND' ValueExpression
Or ::= ValueExpression 'OR' ValueExpression
The supported input types and corresponding return types are as follows:
Operator  type of A (and B)  Return Type 

A + BA  BA * BA / BA % B 
numeric  numeric* 
 A (unary minus) 
numeric  type of A 
A = BA <> B 
numeric, string, boolean, date, time [with time zone], timestamp [with time zone], vertex, edge 
boolean 
A < BA > BA <= BA >= B 
numeric, string, boolean, date, time [with time zone], timestamp [with time zone] 
boolean 
NOT AA AND BA OR B 
boolean  boolean 
Binary operations are only allowed if both operands are of the same type, with the following two exceptions:
 time values can be compared to time with time zone values
 timestamp values can be compared to timestamp with time zone values
To compare such time(stamp) with time zone values to other time(stamp) values (with or without time zone), values are first normalized to have the same time zone, before they are compared. Comparison with other operand type combinations, such as dates and timestamp, is not possible. However, it is possible to cast between e.g. dates and timestamps (see CAST Function).
Operator Precedence
Operator precedences are shown in the following list, from the highest precedence to the lowest. An operator on a higher level (e.g. level 1) is evaluated before an operator on a lower level (e.g. level 2).
Level  Operator Precedence 

1   (unary minus) 
2  * , / , % 
3  + ,  
4  = , <> , > , < , >= , <= 
5  NOT 
6  AND 
7  OR 
Implicit Type Conversion
Performing arithmetic operations with different numeric types will lead to implicit type conversion (i.e. coercion).
Coercion is only defined for numeric types. Given a binary arithmetic operation (i.e. +
, 
, *
, /
, %
), the rules are as follows:
 If both operands are exact numerics (e.g. integer or long), then the result is also an exact numeric with a scale that is at least as large as the scales of each operand.
 If one or both of the operands is approximate numeric (e.g. float, double), the result is an approximate numeric with a scale that is at least as large as the scales of each operand. The precision will also be at least as high as the precision of each operand.
Null values
The property graph data model does not allow properties with null
value. Instead, missing or undefined data can be modeled through the absence of properties.
A null
value is generated when trying to access a property of a vertex or edge wile the property appears to be missing.
Threevalued logic applies when null
values appear in computation.
ThreeValued Logic
An operator returns null
if one of its operands yields null
, with an exception for AND
and OR
. This is shown in the following table:
Operator  Result when A is null  Result when B is null  Result when A and B are null 

A +  * / % B 
null 
null 
null 
 A 
null 
N/A  N/A 
A = <> > < >= <= B 
null 
null 
null 
A AND B 
false if B yields false , null otherwise 
false if A yields false , null otherwise 
null 
A OR B 
true if B yields true , null otherwise 
true if A yields true , null otherwise 
null 
NOT A 
null 
N/A  N/A 
Note that from the table it follows that null = null
yields null
and not true
.
IS NULL and IS NOT NULL
To test whether a value exists or not, one can use the IS NULL
and IS NOT NULL
constructs.
IsNullPredicate ::= ValueExpression 'IS' 'NULL'
IsNotNullPredicate ::= ValueExpression 'IS' 'NOT' 'NULL'
For example:
SELECT n.name
FROM g MATCH (n)
WHERE n.name IS NOT NULL
Here, we find all the vertices in the graph that have the property name
and then return the property.
String functions
JAVA_REGEXP_LIKE
The JAVA_REGEXP_LIKE returns whether the string matches the given Java regular expression pattern.
The syntax is:
JAVA_REGEXP_LIKE( string, pattern )
For example:
JAVA_REGEXP_LIKE('aaaaab', 'a*b')
Result: true
Numeric functions
ABS
The ABS function returns the absolute value of a number. The function returns the same datatype as the numeric datatype of the argument.
The syntax is:
ABS( number )
For example:
ABS(23)
Result: 23
ABS(23.6)
Result: 23.6
ABS(23.65)
Result: 23.65
ABS(23.65)
Result: 23.65
ABS(23.65 * 1)
Result: 23.65
CEIL or CEILING
The CEIL and CEILING functions round the specified number up, and return the smallest number that is greater than or equal to the specified number. The function returns the same datatype as the numeric datatype of the argument.
The syntax is:
CEIL ( number )
CEILING ( number )
For example:
CEIL(3.2)
Result: 4.0
CEIL(2.8)
Result: 3.0
CEIL(3)
Result: 3
FLOOR
The floor function returns the largest integer value that is smaller than or equal to the given argument. The function returns the same datatype as the numeric datatype of the argument.
The syntax is:
FLOOR( number )
For example:
FLOOR(3.2)
Result: 3.0
FLOOR(2.8)
Result: 2.0
FLOOR(3)
Result: 3
ROUND
The round function returns the integer closest to the given argument. The function returns the same datatype as the numeric datatype of the argument.
The syntax is:
ROUND ( number )
For example:
ROUND(3.2)
Result: 3.0
ROUND(2.8)
Result: 3.0
ROUND(3)
Result: 3
Datetime functions
EXTRACT
The EXTRACT
function allows for extracting a datetime field, such as a year, month or day, from a datetime value.
The syntax is:
ExtractFunction ::= 'EXTRACT' '(' ExtractField 'FROM' ValueExpression ')'
ExtractField ::= 'YEAR'
 'MONTH'
 'DAY'
 'HOUR'
 'MINUTE'
 'SECOND'
 'TIMEZONE_HOUR'
 'TIMEZONE_MINUTE'
The fields YEAR
, MONTH
and DAY
can be extracted from a date, a timestamp, or a timestamp with time zone.
For example:
EXTRACT(YEAR FROM DATE '20170213')
Result: 2017
EXTRACT(MONTH FROM DATE '20170213')
Result: 2
EXTRACT(DAY FROM DATE '20170213')
Result: 13
The fields HOUR
, MINUTE
and SECOND
can be extracted from a time, a timestamp, a time with time zone, or a timestamp with time zone.
For example:
EXTRACT(HOUR FROM TIME '12:05:03.201')
Result: 12
EXTRACT(MINUTE FROM TIME '12:05:03.201')
Result: 5
EXTRACT(SECOND FROM TIME '12:05:03.201')
Result: 3.201
The fields TIMEZONE_HOUR
and TIMEZONE_MINUTE
can be extracted from a time with time zone or a timestamp with time zone.
For example:
EXTRACT(TIMEZONE_HOUR FROM TIMESTAMP '20180101 12:30:0002:30')
Result: 2
EXTRACT(TIMEZONE_MINUTE FROM TIMESTAMP '20180101 12:30:0002:30')
Result: 30
Vertex and Edge functions
ID
The ID functions returns a systemgenerated identifier for the vertex/edge (unique within a graph).
The syntax is:
ID( vertex/edge )
LABEL
The LABEL function returns the label of a vertex or an edge. It is an error if the vertex or edge does not have a label, or, has more than one label. The return type of the function is a string.
The syntax is:
LABEL( vertex/edge )
For example:
SELECT LABEL(e)
FROM g MATCH (n:Person) [e]> (m:Person)
++
 LABEL(e) 
++
 likes 
 knows 
 likes 
++
LABELS
The LABELS function returns the set of labels of a vertex or an edge. If the vertex or edge does not have a label, an empty set is returned. The return type of the function is a set of strings.
The syntax is:
LABELS( vertex/edge )
For example:
SELECT LABELS(n)
FROM g MATCH (n:EmployeeManager)
++
 LABELS(n) 
++
 [Employee] 
 [Manager] 
 [Employee, Manager] 
++
HAS_LABEL
The HAS_LABEL functions returns true if the vertex or edge (first argument) has the given label (second argument), and false otherwise.
The syntax is:
HAS_LABEL( vertex/edge, string )
ALL_DIFFERENT
The ALL_DIFFERENT function returns true if the provided values are all different from each other, and false otherwise. The function is typically used for specifying that a particular set of vertices or edges are all different from each other. However, the function can be used for values of any data type, as long as the provided values can be compared for equality.
The syntax is:
ALL_DIFFERENT( val1, val2, val3, ..., valN )
For example:
SELECT n.id, m.id, o.id
FROM g MATCH (n) > (m) > (o)
WHERE ALL_DIFFERENT( n, m, o )
Note that the above query can be rewritten using nonequality constraints as follows:
SELECT *
FROM g MATCH (n) > (m) < (o) > (n)
WHERE n <> m AND n <> o AND m <> o
Another example is:
ALL_DIFFERENT( 1, 2, 3 )
Result: true
ALL_DIFFERENT( 1, 1.0 )
Result: false
IN_DEGREE
The IN_DEGREE function returns the number of incoming neighbors of a vertex. The return type is an exact numeric.
The syntax is:
IN_DEGREE( vertex )
OUT_DEGREE
The OUT_DEGREE function returns the number of outgoing neighbors of a vertex. The return type is an exact numeric.
The syntax is:
OUT_DEGREE( vertex )
UserDefined functions
Userdefined functions (UDFs) are invoked similarly to builtin functions. For example, a user may have registered a function math.tan
that returns the tangent of a given angle.
An example invocation of this function is then:
SELECT math.tan(n.angle) AS tangent
FROM g MATCH (n)
ORDER BY tangent
The syntax is:
FunctionInvocation ::= PackageSpecification? FunctionName '(' ArgumentList? ')'
PackageSpecification ::= PackageName '.'
PackageName ::= IDENTIFIER
FunctionName ::= IDENTIFIER
ArgumentList ::= ValueExpression ( ',' ValueExpression )*
Note that a function invocation has an optional package name, a (nonoptional) function name, and, zero or more arguments which are arbitrary value expressions.
Function and package names are caseinsensitive such that e.g. in_degree(..)
is the same as In_Degree(..)
or IN_DEGREE(..)
.
If a UDF is registered that has the same name as a builtin function, then, upon function invocation, the UDF is invoked and not the builtin function. UDFs can thus override builtins.
CAST
While implicity type conversion is supported between numeric types, between time types, and between timezone types, other type conversions require explicit conversion through casting (CAST
).
The syntax is:
CastSpecification ::= 'CAST' '(' ValueExpression 'AS' DataType ')'
DataType ::= 'STRING'
 'BOOLEAN'
 'INTEGER'
 'INT'
 'LONG'
 'FLOAT'
 'DOUBLE'
 'DATE'
 'TIME'
 'TIME WITH TIME ZONE'
 'TIMESTAMP'
 'TIMESTAMP WITH TIME ZONE'
For example:
SELECT CAST(n.age AS STRING), CAST('123' AS INTEGER), CAST('09:15:00+01:00' AS TIME WITH TIME ZONE)
FROM g MATCH (n:Person)
Casting is allowed between the following data types:
From \ To  string  exact numeric  approximate numeric  boolean  time  time with time zone  date  timestamp  timestamp with time zone 

string  Y  Y  Y  Y  Y  Y  Y  Y  Y 
exact numeric  Y  M  M  N  N  N  N  N  N 
approximate numeric  Y  M  M  N  N  N  N  N  N 
boolean  Y  N  N  Y  N  N  N  N  N 
date  Y  N  N  N  N  N  Y  Y  Y 
time  Y  N  N  N  Y  Y  N  Y  Y 
timestamp  Y  N  N  N  Y  Y  Y  Y  Y 
time with time zone  Y  N  N  N  Y  Y  N  Y  Y 
timestamp with time zone  Y  N  N  N  Y  Y  Y  Y  Y 
In the table above, Y
indicates that casting is supported, N
indicates that casting is not supported, and M
indicates that casting is supported only if the numeric value is within the precision bounds of the specified target type.
CASE
The CASE
predicate returns an expression based on the evaluation of some given Boolean conditions.
There are two types of CASE
expressions: “simple case” and “searched case”.
The syntax is:
CaseExpression ::= SimpleCase  SearchedCase
SimpleCase ::= 'CASE' ValueExpression WhenClause+ ElseClause? 'END'
SearchedCase ::= 'CASE' WhenClause+ ElseClause? 'END'
WhenClause ::= 'WHEN' ValueExpression 'THEN' ValueExpression
ElseClause ::= 'ELSE' ValueExpression
The simple case provides a list of pairs (WHEN
compare value, THEN
return value) and optionally
an else clause (ELSE
return value). PGQL compares a given expression to each compare value and
returns the corresponding return value when compared expressions are equal. If no equal expression
is found and an ELSE
clause exists, then PGQL returns the given else value. If no ELSE
clause
exists, null is returned.
For example:
CASE n.age
WHEN 1 THEN "One"
WHEN 2 THEN "Two"
WHEN 3 THEN "Three"
ELSE "Older than three"
END
The searched case provides a list of pairs (WHEN
boolean expression, THEN
return value) and optionally
an else
clause (ELSE
return value). PGQL evaluates each boolean expression until one of them evaluates
to true, and returns the corresponding return value. If no expression evaluates to true, and an ELSE
clause exists, then PGQL returns the given else value. If no ELSE
clause exists, null is returned.
For example:
CASE
WHEN n.level = 'user' THEN 0
WHEN n.authorized THEN 1
ELSE 1
END
IN and NOT IN
The IN
and NOT IN
predicates test a value for membership in a list of values.
The PGQL literal types INTEGER
, DECIMAL
, BOOLEAN
, STRING
, DATE
, TIME [WITH TIME ZONE]
, TIMESTAMP [WITH TIME ZONE]
are allowed in the list.
The syntax is:
InPredicate ::= ValueExpression 'IN' InValueList
NotInPredicate ::= ValueExpression 'NOT' 'IN' InValueList
InValueList ::= '(' ValueExpression ( ',' ValueExpression )* ')'
 BindVariable
For example:
2 IN (2, 3, 5)
Result: true
3.2 IN (5, 4.8, 3.2)
Result: true
false IN (true, true)
Result: false
'Emily' IN ('Emily', 'Carl')
Result: true
DATE '19900703' IN (DATE '19900703', DATE '19930528')
Result: true
TIME '12:00:10' IN (TIME '11:55:10', TIME '06:50:00.999+05:00')
Result: false
TIMESTAMP '20160320 22:09:59.999' IN (TIMESTAMP '20160320 23:09:59')
Result: false
Bind variables are also supported in the position of the list. For example:
SELECT n.date_of_birth
FROM g MATCH (n:Person)
WHERE n.date_of_birth IN ? /* use PreparedStatement.setArray(int, java.util.List) */
Subqueries
There are two types of subqueries:
Both types of subqueries can be used as a value expression in a SELECT
, WHERE
, GROUP BY
, HAVING
and ORDER BY
clauses (including WHERE
clauses of PATH
expressions). An EXISTS
or NOT EXISTS
subquery returns a boolean while a scalar subquery returns a value of any of the supported data types.
EXISTS and NOT EXISTS subqueries
EXISTS
returns true/false depending on whether the subquery produces at least one result, given the bindings obtained in the current (outer) query. No additional binding of variables occurs.
The syntax is:
An example is to find friend of friends, and, for each friend of friend, return the number of common friends:
SELECT fof.name, COUNT(friend) AS num_common_friends
FROM g MATCH (p:Person) [:has_friend]> (friend:Person) [:has_friend]> (fof:Person)
WHERE NOT EXISTS (
SELECT *
FROM g
MATCH (p) [:has_friend]> (fof)
)
Here, vertices p
and fof
are passed from the outer query to the inner query. The EXISTS
returns true if there is at least one has_friend
edge between vertices p
and fof
.
Users can add a subquery in the WHERE
clause of the PATH
definition. One might be interested in asserting for specific properties for a vertex in the PATH
. The following example defines a path ending in a vertex which is not the oldest in the graph:
PATH p AS (a) > (b) WHERE EXISTS ( SELECT * FROM g MATCH (x) WHERE x.age > b.age )
SELECT ...
FROM ...
Topology related constraints can also be imposed. The following example defines a path ending in a vertex which has at least one outgoing edge to some neighbor c
:
PATH p AS (a) > (b) WHERE EXISTS ( SELECT * FROM g MATCH (b) > (c) )
SELECT ...
FROM ...
Scalar subqueries
Scalar subqueries are queries that return a scalar value (exactly one row and exactly one column) such that they can be part of an expression in a SELECT
, WHERE
, GROUP BY
, HAVING
or ORDER BY
clause.
The syntax is:
ScalarSubquery ::= Subquery
For example:
SELECT a.name
FROM g MATCH (a)
WHERE a.age > ( SELECT AVG(b.age) FROM g MATCH (a) [:friendOf]> (b) )
Another example is:
SELECT p.name AS name
, ( SELECT SUM(t.amount)
FROM financial_transactions
MATCH (a) <[t:transaction] (:Account)
) AS sum_incoming
, ( SELECT SUM(t.amount)
FROM financial_transactions
MATCH (a) [t:transaction]> (:Account)
) AS sum_outgoing
, ( SELECT COUNT(DISTINCT p2)
FROM financial_transactions
MATCH (a) [t:transaction] (:Account) <[:ownerOf] (p2:Person)
WHERE p2 <> p
) AS num_persons_transacted_with
, ( SELECT COUNT(DISTINCT c)
FROM financial_transactions
MATCH (a) [t:transaction] (:Account) <[:ownerOf] (c:Company)
) AS num_companies_transacted_with
FROM financial_transactions
MATCH (p:Person) [:ownerOf]> (a:Account)
ORDER BY sum_outgoing + sum_incoming DESC
++
 name  sum_incoming  sum_outgoing  num_persons_transacted_with  num_companies_transacted_with 
++
 Liam  9999.5  9900.0  1  1 
 Camille  9900.0  1000.0  2  0 
 Nikita  1000.0  4501.0  1  1 
++
Note that in the query, the graph name financial_transactions
is repeatedly specified. Such repetition may be avoided by relying on a default graph such that the query can be simplified to:
SELECT p.name AS name
, ( SELECT SUM(t.amount)
MATCH (a) <[t:transaction] (:Account)
) AS sum_incoming
, ( SELECT SUM(t.amount)
MATCH (a) [t:transaction]> (:Account)
) AS sum_outgoing
, ( SELECT COUNT(DISTINCT p2)
MATCH (a) [t:transaction] (:Account) <[:ownerOf] (p2:Person)
WHERE p2 <> p
) AS num_persons_transacted_with
, ( SELECT COUNT(DISTINCT c)
MATCH (a) [t:transaction] (:Account) <[:ownerOf] (c:Company)
) AS num_companies_transacted_with
MATCH (p:Person) [:ownerOf]> (a:Account)
ORDER BY sum_outgoing + sum_incoming DESC
Other Syntactic rules
Identifiers
Identifiers (used for e.g. graph names, property names, etc.) take the form of an alphabetic character followed by zero or more alphanumeric or underscore (i.e. _
) characters.
The syntax is:
TODO: update.
Special characters in property names, graph names, and labels
Identifiers like graph names, property names, and labels can be delimited with double quotes to allow for encoding of special characters (e.g. the space in the property name n."my prop"
).
Any Unicode character may be used inside the delimiters.
Lexical constructs for literals
The following are the lexical grammar constructs:
SINGLE_QUOTED_STRING ::= "'" ( ~[\'\n\\]  ESCAPED_CHARACTER )* "'"
UNSIGNED_INTEGER ::= [09]+
UNSIGNED_DECIMAL ::= ( [09]* '.' [09]+ )  ( [09]+ '.' )
These rules describe the following:
 Single quoted strings (used for string literals) consist of:
 A starting single quote.
 Any number of characters that are either:
 Not single quote characters, new line characters, or backslash characters.
 Escaped characters.
 An ending single quote.
 Unsigned integers consist of one or more digits.
 Unsigned decimals consist of zero or more digits followed by a dot (
.
) and one or more digits, or, one or more digits followed by only a dot (.
).
Escaped characters
Escaping in string literals and identifiers is necessary to support white space, quotation marks, and backslash characters.
The syntax is:
TODO: fix the grammar.
Note that an escaped character is either a tab (\t
), a line feed (\n
), a carriage return (\r
), a single (\'
) or double quote (\"
), or a backslash (\\
). Corresponding Unicode code points are shown in the table below.
Escape  Unicode code point 

\t 
U+0009 (tab) 
\n 
U+000A (line feed) 
\r 
U+000D (carriage return) 
\" 
U+0022 (quotation mark, double quote mark) 
\' 
U+0027 (apostrophequote, single quote mark) 
\\ 
U+005C (backslash) 
TODO: fix the table.
In string literals, it is optional to escape double quotes.
For example:
'abc\"d\"efg' = 'abc"d"efg'
Result: true
In addition to Javalike escaping, string literals in PGQL queries can be escaped in a SQLlike fashion by repeating the quote.
For example, n.prop = 'string''value'
is an alternative for n.prop = 'string\'value'
, and FROM "my""graph"
is an alternative for FROM "my\"graph"
.
Keywords
The following is a list of keywords in PGQL.
PATH, SELECT, FROM, MATCH, WHERE, GROUP, BY,
HAVING, ORDER, ASC, DESC, LIMIT, OFFSET,
AND, OR, NOT, true, false, IS, NULL, AS,
DATE, TIME, TIMESTAMP, WITH, ZONE, DISTINCT,
COUNT, MIN, MAX, AVG, SUM, ARRAY_AGG, IN,
EXISTS, CAST, CASE, WHEN, THEN, ELSE, END,
EXTRACT, YEAR, MONTH, DAY, HOUR, MINUTE,
SECOND, TIMEZONE_HOUR, TIMEZONE_MINUTE,
TOP, SHORTEST
Keywords are caseinsensitive and variations such as SELECT
, Select
and sELeCt
can be used interchangeably.
Comments
Comments are delimited by /*
and */
.
The syntax is:
For example:
/* This is a
multiline
comment. */
SELECT n.name, n.age
FROM g MATCH (n:Person) /* this is a singleline comment */