3.3. Clauses

This section contains information on all the clauses in the Cypher query language.

Reading clauses

These comprise clauses that read data from the database.

The flow of data within a Cypher query is an unordered sequence of maps with key-value pairs — a set of possible bindings between the variables in the query and values derived from the database. This set is refined and augmented by subsequent parts of the query.

Clause Description

MATCH

Specify the patterns to search for in the database.

OPTIONAL MATCH

Specify the patterns to search for in the database while using nulls for missing parts of the pattern.

START

Find starting points through legacy indexes.

Projecting clauses

These comprise clauses that define which expressions to return in the result set.

Clause Description

RETURN

Defines what to include in the query result set.

WITH

Allows query parts to be chained together, piping the results from one to be used as starting points or criteria in the next.

UNWIND

Expands a list into a sequence of rows.

Reading sub-clauses

These comprise sub-clauses that must operate as part of reading clauses.

Sub-clause Description

WHERE

Adds constraints to the patterns in a MATCH or OPTIONAL MATCH clause or filters the results of a WITH clause.

ORDER BY

A sub-clause following RETURN or WITH, specifying that the output should be sorted in particular way.

SKIP

Defines from which row to start including the rows in the output.

LIMIT

Constrains the number of rows in the output.

Reading hints

These comprise clauses used to specify planner hints when tuning a query. More details regarding the usage of these — and query tuning in general — can be found in Section 3.6.4, “Planner hints and the USING keyword”.

Hint Description

USING INDEX

Index hints are used to specify which index, if any, the planner should use as a starting point.

USING SCAN

Scan hints are used to force the planner to do a label scan (followed by a filtering operation) instead of using an index.

USING JOIN

Join hints are used to enforce a join operation at specified points.

Writing clauses

These comprise clauses that write the data to the database.

Clause Description

CREATE

Create nodes and relationships.

DELETE

Delete graph elements — nodes, relationships or paths. Any node to be deleted must also have all associated relationships explicitly deleted.

DETACH DELETE

Delete a node or set of nodes. All associated relationships will automatically be deleted.

SET

Update labels on nodes and properties on nodes and relationships.

REMOVE

Remove properties and labels from nodes and relationships.

FOREACH

Update data within a list, whether components of a path, or the result of aggregation.

Reading/Writing clauses

These comprise clauses that both read data from and write data to the database.

Clause Description

MERGE

Ensures that a pattern exists in the graph. Either the pattern already exists, or it needs to be created.

--- ON CREATE

Used in conjunction with MERGE, this write sub-clause specifies the actions to take if the pattern needs to be created.

--- ON MATCH

Used in conjunction with MERGE, this write sub-clause specifies the actions to take if the pattern already exists.

CALL…​YIELD

Invoke a procedure deployed in the database and return any results.

CREATE UNIQUE

A mixture of MATCH and CREATE, matching what it can, and creating what is missing.

Set operations

Clause Description

UNION

Combines the result of multiple queries into a single result set. Duplicates are removed.

UNION ALL

Combines the result of multiple queries into a single result set. Duplicates are retained.

Importing data

Clause Description

LOAD CSV

Use when importing data from CSV files.

--- USING PERIODIC COMMIT

This query hint may be used to prevent an out-of-memory error from occurring when importing large amounts of data using LOAD CSV.

Schema clauses

These comprise clauses used to manage the schema; further details can found in Section 3.5, “Schema”.

Clause Description

CREATE | DROP CONSTRAINT

Create or drop an index on all nodes with a particular label and property.

CREATE | DROP INDEX

Create or drop a constraint pertaining to either a node label or relationship type, and a property.