Overview

This section provides an overview of Cypher® and a brief discussion of how Cypher differs to SQL.

What is Cypher?

Cypher is Neo4j’s declarative graph query language. It was created in 2011 by Neo4j engineers as an SQL-equivalent language for graph databases. Similar to SQL, Cypher lets users focus on what to retrieve from graph, rather than how to retrieve it. As such, Cypher enables users to realize the full potential of their property graph databases by allowing for efficient and expressive queries that reveal previously unknown data connections and clusters.

Cypher provides a visual way of matching patterns and relationships. It relies on the following ascii-art type of syntax: (nodes)-[:CONNECT_TO]→(otherNodes). Rounded brackets are used for circular nodes, and -[:ARROWS]→ for relationships. Writing a query is effectively like drawing a pattern through the data in the graph. In other words, entities such as nodes and their relationships are visually built into queries. This makes Cypher a highly intuitive language to both read and write.

Cypher and SQL: key differences

Cypher and SQL are similar in many ways. For example, they share many of the same keywords, such as WHERE and ORDER BY. However, there are some important differences between the two:

Cypher is schema-flexible

While it is both possible and advised to enforce partial schemas using indexes and constraints, Cypher and Neo4j offers a greater degree of schema-flexibility than SQL and a relational database. More specifically, nodes and relationships in a Neo4j database do not have to have a specific property set to them because other nodes or relationships in the same graph have that property (unless there is an property existence constraint created on that specific property). This means that users are not required to use a fixed schema to represent data and that they can add new attributes and relationships as their graphs evolve.

Query order

SQL queries begin with what a user wants to return, whereas Cypher queries end with the return clause. For example, consider the following two queries (both searching a database for titles of movies with a rating of greater than 7), the first written with SQL and the second with Cypher:

SELECT movie.name
FROM movie
WHERE movie.rating > 7
MATCH (movie:Movie)
WHERE movie.rating > 7
RETURN movie.title
Cypher queries are more concise

Due to its intuitive, whiteboard-like method of constructing clauses, Cypher queries are often more concise than their equivalent SQL queries. For example, consider the following two queries (both searching a database for the names of the actors in the movie The Matrix), the first written with SQL and the second with Cypher:

SELECT actors.name
FROM actors
 	LEFT JOIN acted_in ON acted_in.actor_id = actors.id
	LEFT JOIN movies ON movies.id = acted_in.movie_id
WHERE movies.title = "The Matrix"
MATCH (actor:Actor)-[:ACTED_IN]->(movie:Movie {title: 'The Matrix'})
RETURN actor.name

Cypher and APOC

Neo4j supports the APOC (Awesome Procedures on Cypher) Core library. The APOC Core library provides access to user-defined procedures and functions which extend the use of the Cypher query language into areas such as data integration, graph algorithms, and data conversion.

For more details, visit the APOC Core page.