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‎modules/ROOT/pages/subqueries/call-subquery.adoc‎

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Original file line numberDiff line numberDiff line change
@@ -31,14 +31,9 @@ CREATE (teamA:Team {name: 'Team A'}),
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(playerF:Player {name: 'Player F', age: 35}),
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(playerA)-[:PLAYS_FOR]->(teamA),
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(playerB)-[:PLAYS_FOR]->(teamA),
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(playerC)-[:PLAYS_FOR]->(teamA),
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(playerD)-[:PLAYS_FOR]->(teamB),
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(playerE)-[:PLAYS_FOR]->(teamC),
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(playerF)-[:PLAYS_FOR]->(teamC),
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(playerA)-[:FRIEND_OF]->(playerB),
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(playerA)-[:FRIEND_OF]->(playerC),
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(playerB)-[:FRIEND_OF]->(playerF),
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(playerC)-[:FRIEND_OF]->(playerD),
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(teamA)-[:OWES {dollars: 1500}]->(teamB),
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(teamA)-[:OWES {dollars: 3000}]->(teamB),
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(teamB)-[:OWES {dollars: 1700}]->(teamC),
@@ -93,7 +88,6 @@ CALL () {
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SET p.age = p.age + 1
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RETURN p.age AS newAge
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}
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WITH x, newAge
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MATCH (p:Player {name: 'Player A'})
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RETURN x AS iteration, newAge, p.age AS totalAge
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----
@@ -140,7 +134,7 @@ RETURN t AS team, players
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| players
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| (:Team {name: "Team A"})
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| [(:Player {name: "Player C", age: 19}), (:Player {name: "Player B", age: 23}), (:Player {name: "Player A", age: 24})]
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| (:Player {name: "Player B", age: 23}), (:Player {name: "Player A", age: 24})]
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| (:Team {name: "Team B"})
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| [(:Player {name: "Player D", age: 30})]
@@ -161,7 +155,6 @@ Using a `CALL` subquery can therefore reduce the amount of heap memory required
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Variables from the outer scope must be explicitly imported into the inner scope of the `CALL` subquery, either by using a xref:subqueries/call-subquery.adoc#variable-scope-clause[variable scope clause] or an xref:subqueries/call-subquery.adoc#importing-with[importing `WITH` clause] (deprecated).
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As the subquery is evaluated for each incoming input row, the imported variables are assigned the corresponding values from that row.
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164-
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[[variable-scope-clause]]
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=== The variable scope clause
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@@ -279,7 +272,7 @@ RETURN count(t) AS totalTeams, totalPlayers
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[NOTE]
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=====
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As of Neo4j 5.23, it is deprecated to use `CALL` subqueries without a variable scope clause.
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`CALL` subqueries without a variable scope clause are deprecated.
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.Deprecated
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[source, cypher]
@@ -423,7 +416,6 @@ RETURN largeLists
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====
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[[optional-call]]
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== Optional subquery calls
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@@ -433,60 +425,60 @@ Similar to xref:clauses/optional-match.adoc[`OPTIONAL MATCH`] any empty rows pro
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.Difference between using `CALL` and `OPTIONAL CALL`
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====
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This example, which finds the friends of each `Player` and xref:functions/aggregating.adoc#functions-count[counts] the number of friends per player, highlights the difference between using `CALL` and `OPTIONAL CALL`.
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This example, which finds the team that each `Player` plays for, highlights the difference between using `CALL` and `OPTIONAL CALL`.
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.Regular subquery `CALL`
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[source, cypher]
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----
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MATCH (p:Player)
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CALL (p) {
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MATCH (p)-[:FRIEND_OF]->(friend:Player)
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RETURN friend
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MATCH (p)-[:PLAYS_FOR]->(team:Team)
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RETURN team
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}
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RETURN p.name AS playerName, count(friend) AS numberOfFriends
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ORDER BY numberOfFriends
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RETURN p.name AS playerName, team.name AS team
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----
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.Optional subquery `CALL`
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.Result
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[role="queryresult",options="header,footer",cols="2*m"]
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|===
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| playerName | numberOfFriends
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| playerName | team
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| "Player B" | 1
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| "Player C" | 1
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| "Player A" | 2
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| "Player A" | "Team A"
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| "Player B" | "Team A"
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| "Player D" | "Team B"
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| "Player E" | "Team C"
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| "Player F" | "Team C"
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459-
2+d|Rows: 3
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2+d|Rows: 5
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|===
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462-
Note that no results are returned for `Player D`, `Player E`, and `Player F`, since they have no outgoing `FRIEND_OF` relationships connected to them.
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Note that no results are returned for `Player C`, since they are not connected to any `Team` with a `PLAYS_FOR` relationship.
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.Query using regular `OPTIONAL CALL`
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[source, cypher]
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----
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MATCH (p:Player)
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OPTIONAL CALL (p) {
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MATCH (p)-[:FRIEND_OF]->(friend:Player)
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RETURN friend
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MATCH (p)-[:PLAYS_FOR]->(team:Team)
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RETURN team
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}
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RETURN p.name AS playerName, count(friend) AS numberOfFriends
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ORDER BY numberOfFriends
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RETURN p.name AS playerName, team.name AS team
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----
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Now, all `Player` nodes, regardless of whether they have any friends or not, are returned.
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(Those without any outgoing `FRIEND_OF` relationships are returned with the result `0` because `count()` ignores `null` values.)
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Now all `Player` nodes, regardless of whether they have any `PLAYS_FOR` relationships connected to a `Team`, are returned.
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470+
.Result
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.Result
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[role="queryresult",options="header,footer",cols="2*m"]
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|===
482-
| playerName | numberOfFriends
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| playerName | team
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484-
| "Player D" | 0
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| "Player E" | 0
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| "Player F" | 0
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| "Player B" | 1
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| "Player C" | 1
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| "Player A" | 2
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| "Player A" | "Team A"
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| "Player B" | "Team A"
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| "Player C" | NULL
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| "Player D" | "Team B"
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| "Player E" | "Team C"
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| "Player F" | "Team C"
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2+d|Rows: 6
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|===
@@ -496,8 +488,8 @@ Now, all `Player` nodes, regardless of whether they have any friends or not, are
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[[call-execution-order]]
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== Execution order of CALL subqueries
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499-
The order in which subqueries are executed is not defined.
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If a query result depends on the order of execution of subqueries, an `ORDER BY` clause should precede the `CALL` clause.
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The order in which rows from the outer scope are passed into subqueries is not defined.
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If the results of the subquery depend on the order of these rows, use an `ORDER BY` clause before the `CALL` clause to guarantee a specific processing order for the rows.
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.Ordering results before `CALL` subquery
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====
@@ -591,13 +583,13 @@ UNION
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ORDER BY p.age DESC
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LIMIT 1
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}
594-
RETURN p.name AS name, p.age AS age
586+
RETURN p.name AS playerName, p.age AS age
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----
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.Result
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[role="queryresult",options="header,footer",cols="2*<m"]
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|===
600-
| name | age
592+
| playerName | age
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| "Player C" | 19
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| "Player F" | 35
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2+d|Rows: 2
@@ -642,39 +634,33 @@ The result of the `CALL` subquery is the combined result of evaluating the subqu
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643635
.`CALL` subquery changing returned rows of outer query
644636
====
645-
The following example finds the name of each `Player` and the names of their friends.
646-
No rows are returned for the `Player` nodes without any `FRIEND_OF` relationships, the number of results of the subquery thus changed the number of results of the enclosing query.
637+
The following example finds the name of each `Player` and the team they play for.
638+
No rows are returned for `Player C`, since they are not connected to a `Team` with a `PLAYS_FOR` relationship.
639+
The number of results of the subquery thus changed the number of results of the enclosing query.
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648641
.Find the friends of players
649642
[source, cypher]
650643
----
651644
MATCH (p:Player)
652645
CALL (p) {
653-
MATCH (p)-[:FRIEND_OF]->(p2:Player)
654-
RETURN p2.name AS friend
646+
MATCH (p)-[:PLAYS_FOR]->(team:Team)
647+
RETURN team.name AS team
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}
656-
RETURN p.name AS player, friend
649+
RETURN p.name AS playerName, team
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----
658651
659652
.Result
660-
[role="queryresult",options="header,footer",cols="2*<m"]
653+
[role="queryresult",options="header,footer",cols="2*m"]
661654
|===
662-
| player
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| friend
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665-
| "Player A"
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| "Player B"
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668-
| "Player A"
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| "Player C"
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671-
| "Player B"
672-
| "Player F"
655+
| playerName | team
673656
674-
| "Player C"
675-
| "Player D"
657+
| "Player A" | "Team A"
658+
| "Player B" | "Team A"
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| "Player D" | "Team B"
660+
| "Player E" | "Team C"
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| "Player F" | "Team C"
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677-
2+d|Rows: 4
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2+d|Rows: 5
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|===
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====
@@ -772,7 +758,7 @@ Labels added: 18
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* `CALL` subqueries optimize data handling and query efficiency, and can perform changes to the database.
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775-
* `CALL` subqueries enable progressive data transformation and can accumulate results across multiple row executions.
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* `CALL` subqueries allow for row-by-row data transformation and enable the accumulation of results across multiple rows, facilitating complex operations that depend on intermediate or aggregated data.
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* `CALL` subqueries can only refer to variables from the enclosing query if they are explicitly imported by either a variable scope clause or an importing `WITH` clause (deprecated).
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@@ -782,4 +768,4 @@ Labels added: 18
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* An `ORDER BY` clause can be used before `CALL` subqueries to ensure a specific order.
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785-
* `CALL` subqueries can be used in combination with `UNION` to process and aggregate different parts of a query result.
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* `CALL` subqueries can be used in combination with `UNION` to process and aggregate different parts of a query result.

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