Book Image

Graph Data Processing with Cypher

By : Ravindranatha Anthapu
Book Image

Graph Data Processing with Cypher

By: Ravindranatha Anthapu

Overview of this book

While it is easy to learn and understand the Cypher declarative language for querying graph databases, it can be very difficult to master it. As graph databases are becoming more mainstream, there is a dearth of content and guidance for developers to leverage database capabilities fully. This book fills the information gap by describing graph traversal patterns in a simple and readable way. This book provides a guided tour of Cypher from understanding the syntax, building a graph data model, and loading the data into graphs to building queries and profiling the queries for best performance. It introduces APOC utilities that can augment Cypher queries to build complex queries. You’ll also be introduced to visualization tools such as Bloom to get the most out of the graph when presenting the results to the end users. After having worked through this book, you’ll have become a seasoned Cypher query developer with a good understanding of the query language and how to use it for the best performance.
Table of Contents (18 chapters)
1
Part 1: Cypher Introduction
4
Part 2: Working with Cypher
9
Part 3: Advanced Cypher Concepts

Working with UNION in Cypher

The UNION clause combines the results of two or more queries and returns the results. It works pretty similarly to how it works in SQL queries. Normally, we use the UNION clause when we want to combine the results of multiple, disparate queries returning similar datasets.

Let’s look at an example usage of the UNION clause:

MATCH (p:Patient)-[:HAS_ENCOUNTER]->()-[:HAS_DIAGNOSIS]->(d)
WHERE p.id='f237e253-9052-a038-7c9e-dbd9a1d7da32'
RETURN d.code as drug
UNION
MATCH (p:Patient)-[:HAS_ENCOUNTER]->()-[:HAS_DIAGNOSIS]->(d)
WHERE p.id='ffa580de-08e5-9a47-b12a-db312ad6825b'
RETURN d.code as drug

This query returns the diagnosis codes used among two patients, as shown in the following figure:

Figure 6.13 – Usage of the UNION clause

We can see there are five records returned. The UNION clause eliminates duplicate records in the results if there are any.

We could have written the...