Subqueries with CALL { } in Neo4j

1. Introduction

The CALL { } syntax in Neo4j allows you to write subqueries that can encapsulate complex logic within a Cypher query. This feature enhances the modularity of your queries and allows for more efficient data retrieval by executing smaller, reusable query blocks.

2. Key Concepts

• Subquery: A query nested inside another query, providing a way to perform multiple operations within a single execution context.
• CALL: A Cypher command used to invoke procedures and subqueries.
• RETURN: This keyword is used to specify which results to return from the query.

3. Step-by-Step Guide

To create a subquery using CALL { }, follow these steps:

1. Identify the main query context.
2. Define the subquery within CALL { }.
3. Use RETURN to specify the output of the subquery.
4. Integrate the subquery with the main query.

Example

CALL {
    MATCH (n:Person)
    WHERE n.age > 30
    RETURN n.name AS name
}
RETURN name

In this example, we call a subquery that retrieves names of persons older than 30, and then return those names in the main query.

4. Best Practices

When using subqueries with CALL { }, keep these best practices in mind:

• Keep subqueries modular and focused on specific tasks.
• Avoid unnecessary complexity to maintain readability.
• Use aliases effectively to clarify output.
• Test subqueries independently for debugging.

5. FAQ