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Node and relationship operators (neo4j#1241)
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‎modules/ROOT/content-nav.adoc‎

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*** xref:expressions/predicates/string-operators.adoc[]
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*** xref:expressions/predicates/path-pattern-expressions.adoc[]
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*** xref:expressions/predicates/type-predicate-expressions.adoc[]
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** xref:expressions/node-relationship-operators.adoc[]
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** xref:expressions/mathematical-operators.adoc[]
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** xref:expressions/string-operators.adoc[]
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** xref:expressions/temporal-operators.adoc[]

‎modules/ROOT/images/graph_element_operators.svg‎

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‎modules/ROOT/pages/expressions/index.adoc‎

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= Expressions
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:description: Information about the expressions available in Cypher.
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:page-aliases: syntax/operators.adoc
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A Cypher expression is any part of a query that evaluates to a value.
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For details and examples of specific expressions, see the following sections:
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** xref:expressions/predicates/string-operators.adoc[]: `STARTS WITH`, `ENDS WITH`, `CONTAINS`, `IS NORMALIZED`, `IS NOT NORMALIZED`, `=~`
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** xref:expressions/predicates/path-pattern-expressions.adoc[]: information about filtering queries with path pattern expressions.
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** xref:expressions/predicates/type-predicate-expressions.adoc[]: information about how to verify the value type of a Cypher expression.
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* xref:expressions/node-relationship-operators.adoc[]: information about how to access `NODE` and `RELATIONSHIP` property values with `.` and `[]`.
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* xref:expressions/mathematical-operators.adoc[]: `+`, `-`, `*`, `/`, `%`, `^`.
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* xref:expressions/string-operators.adoc[]: `+`, `||`
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* xref:expressions/temporal-operators.adoc[]: `+`, `-`, `*`, `/`
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* xref:expressions/list-expressions.adoc[]: information about list concatenation operators (`||`, `+`), list element access, list slicing, and list as well as pattern comprehensions.
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* xref:expressions/map-expressions.adoc[]: information about map operators (`.`, `[]`) and map projection.
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* xref:expressions/conditional-expressions.adoc[]
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‎modules/ROOT/pages/expressions/node-relationship-operators.adoc‎

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= Node and relationship operators
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:description: Information about Cypher's node and relationship operators, which enable the querying and manipulation of nodes and relationships.
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Node and relationship operators allow you to manipulate and query `NODE` and `RELATIONSHIP` property values.
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Cypher contains the following node and relationship operators:
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* Static property access: dot operator (`.`)
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* Dynamic property access: subscript operator (`[]`)
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For functions that return metadata about `NODE` and `RELATIONSHIP` values, see:
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* xref:functions/scalar.adoc#functions-elementid[`elementId()`]
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* xref:functions/scalar.adoc#functions-endnode[`endNode()`]
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* xref:functions/scalar.adoc#functions-id[`id()`]
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* xref:functions/list.adoc#functions-keys[`keys()`]
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* xref:functions/list.adoc#functions-labels[`labels()`]
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* xref:functions/scalar.adoc#functions-properties[`properties()`]
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* xref:functions/scalar.adoc#functions-startnode[`startNode()`]
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* xref:functions/scalar.adoc#functions-type[`type()`]
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[[example-graph]]
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== Example graph
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The following graph is used for the examples below:
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image::graph_element_operators.svg[width="600",role="middle"]
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To recreate the graph, run the following query against an empty Neo4j database:
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[source, cypher, role=test-setup]
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----
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CREATE (alice:Person {firstName:'Alice', middleName: 'Catherine', lastName: 'Baxter'}),
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(cecil:Person {firstName: 'Cecil', middleName: 'David', lastName: 'Ericson'}),
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(cecilia:Person {firstName: 'Cecilia', lastName: 'Farega'}),
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(cecil)-[:WORKS_FOR {since: 2023}]->(alice),
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(cecilia)-[:WORKS_FOR {since: 2015}]->(alice)
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----
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[[static-property-access]]
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== Static property access
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Property values can be accessed statically by specifying a property name after the `.` operator.
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.Access node properties statically
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[source, cypher]
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----
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MATCH (p:Person)
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RETURN p.firstName AS name
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----
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.Result
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[role="queryresult",options="header,footer",cols="1*<m"]
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|===
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| name
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| "Alice"
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| "Cecil"
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| "Cecilia"
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1+d|Rows: 3
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|===
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.Access node and relationship properties statically
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[source, cypher]
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----
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MATCH (employee:Person)-[r:WORKS_FOR]-(manager:Person)
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RETURN employee.firstName AS employee,
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r.since AS employedSince,
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manager.firstName AS manager
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----
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.Result
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[role="queryresult",options="header,footer",cols="3*<m"]
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|===
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| employee | employedSince | manager
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| "Cecil" | 2023 | "Alice"
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| "Cecilia" | 2015 | "Alice"
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3+d|Rows: 2
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|===
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[[dynamic-property-access]]
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== Dynamic property access
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Property values can be accessed dynamically by using the subscript operator, `[]`.
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.Access properties dynamically using a variable
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[source, cypher]
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----
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LET nodeProperty = 'lastName'
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MATCH (p:Person)
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RETURN p[nodeProperty] AS lastName
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----
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.Result
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[role="queryresult",options="header,footer",cols="1*<m"]
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|===
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| lastName
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| "Baxter"
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| "Ericson"
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| "Farega"
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1+d|Rows: 3
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|===
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.Parameters
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[source, parameters]
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----
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{
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"propertyName": 'middleName'
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}
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----
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.Access properties dynamically using a parameter
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[source, cypher]
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----
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MATCH (:Person)
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RETURN p[$propertyName] AS middleName
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----
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.Result
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[role="queryresult",options="header,footer",cols="1*<m"]
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|===
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| middleName
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| "Catherine"
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| "David"
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| NULL
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1+d|Rows: 3
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|===
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== Handling `NULL` values
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If a property (or property value) is missing in an expression that uses tries to access a property statically or dynamically, the whole expression will evaluate to `NULL`.
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The query below performs a xref:expressions/string-operators.adoc[string concatentation] on the `firstName`, `middleName`, and `lastName` properties on `Person` nodes.
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Note that `NULL` is returned for `Cecilia`, who lacks a `middleName` property.
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.String concatenation using node properties
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[source, cypher]
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----
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MATCH (p:Person)
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RETURN p.firstName || ' ' || p.middleName || ' ' || p.lastName AS fullName
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----
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.Result
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[role="queryresult",options="header,footer",cols="1*<m"]
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|===
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| fullName
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| "Alice Catherine Baxter"
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| "Cecil David Ericson"
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| NULL
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1+d|Rows: 3
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|===
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The xref:functions/scalar.adoc#functions-coalesce[`coalesce()`] function can be used to skip the first `NULL` values in an expression.
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In the below example, it replaces the first `NULL` value found with an empty `STRING`.
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.Use the `coalesce()` function to skip `NULL` values
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[source, cypher]
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----
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MATCH (p:Person)
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RETURN p.firstName || coalesce(' ' + p.middleName, '') || ' ' || p.lastName AS fullName
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----
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.Result
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[role="queryresult",options="header,footer",cols="1*<m"]
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|===
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| fullName
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| "Alice Catherine Baxter"
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| "Cecil David Ericson"
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| "Cecilia Farega"
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1+d|Rows: 3
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|===

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