The following subqueries are supported in GQL query statements:
Subquery list
Name | Summary |
---|---|
ARRAY subquery
|
Subquery expression that produces an array. |
EXISTS subquery
|
Checks if a subquery produces at least one row. |
IN subquery
|
Checks if a subquery produces a specified value. |
VALUE subquery
|
Subquery expression that produces a scalar value. |
ARRAY
subquery
ARRAY { gql_query_expr }
Description
Subquery expression that produces an array. If the subquery produces zero rows,
an empty array is produced. Never produces a NULL
array. This can be used
wherever a query expression is supported in a GQL query statement.
Definitions
gql_query_expr
: A GQL query expression.
Return type
ARRAY<T>
Examples
In the following query, an array of transfer amounts is produced for each
Account
owned by each Person
node:
GRAPH FinGraph
MATCH (p:Person)-[:Owns]->(account:Account)
RETURN
p.name, account.id AS account_id,
ARRAY {
MATCH (a:Account)-[transfer:Transfers]->(:Account)
WHERE a = account
RETURN transfer.amount AS transfers
} AS transfers;
/*-------------------------------+
| name | account_id | transfers |
+-------------------+-----------+
| Alex | 7 | [300,100] |
| Dana | 20 | [500,200] |
| Lee | 16 | [300] |
+-------------------------------*/
EXISTS
subquery
EXISTS { gql_query_expr }
EXISTS { match_statement }
EXISTS { graph_pattern }
Description
Checks if the subquery produces at least one row. Returns TRUE
if
at least one row is produced, otherwise returns FALSE
. Never produces NULL
.
Definitions
gql_query_expr
: A GQL query expression.match_statement
: A pattern matching operation to perform on a graph. For more information, seeMATCH
statement.graph_pattern
: A pattern to match in a graph. For more information, see graph pattern definition.
Return type
BOOL
Examples
The following query checks whether any Person
whose name starts with the
letter 'D'
owns an Account
. The subquery contains a graph query expression.
GRAPH FinGraph
RETURN EXISTS {
MATCH (p:Person)-[o:Owns]->(a:Account)
WHERE p.Name LIKE 'D%'
RETURN p.Name
LIMIT 1
} AS results;
/*---------+
| results |
+---------+
| true |
+---------*/
You can include a MATCH
statement or a graph pattern in an EXISTS
subquery. The following examples include two ways to construct the subquery
and produce similar results:
GRAPH FinGraph
RETURN EXISTS {
MATCH (p:Person)-[o:Owns]->(a:Account)
WHERE p.Name LIKE 'D%'
} AS results;
/*---------+
| results |
+---------+
| true |
+---------*/
GRAPH FinGraph
RETURN EXISTS {
(p:Person)-[o:Owns]->(a:Account) WHERE p.Name LIKE 'D%'
} AS results;
/*---------+
| results |
+---------+
| true |
+---------*/
IN
subquery
value [ NOT ] IN { gql_query_expr }
Description
Checks if value
is present in the subquery result. Returns TRUE
if the
result contains the value
, otherwise returns FALSE
.
Definitions
value
: The value look for in the subquery result.IN
:TRUE
if the value is in the subquery result, otherwiseFALSE
.NOT IN
:FALSE
if the value is in the subquery result, otherwiseTRUE
.gql_query_expr
: A GQL query expression.
Details
The subquery result must have a single column and that column type must
be comparable to the value
type. If not, an error is returned.
Return type
BOOL
Examples
The following query checks if 'Dana'
is a name of a person who owns an
account.
GRAPH FinGraph
RETURN 'Dana' IN {
MATCH (p:Person)-[o:Owns]->(a:Account)
RETURN p.name
} AS results;
/*---------+
| results |
+---------+
| true |
+---------*/
VALUE
subquery
VALUE { gql_query_expr }
Description
A subquery expression that produces a scalar value.
Definitions
gql_query_expr
: A GQL query expression.
Details
The result of the subquery must have a single column. If the subquery returns
more than one column, the query fails with an analysis error. The result type of
the subquery expression is the produced column type. If the subquery produces
exactly one row, that single value is the subquery expression result. If the
subquery returns zero rows, the subquery expression result is NULL
. If the
subquery returns more than one row, the query fails with a runtime error.
Return type
The same as the column type in the subquery result.
Examples
The following query returns a the name of any Person
whose name contains the
character 'e'
:
GRAPH FinGraph
RETURN VALUE {
MATCH (p:Person)
WHERE p.name LIKE '%e%'
RETURN p.name
LIMIT 1
} AS results;
/*---------+
| results |
+---------+
| [Alex] |
+---------*/