GraphAcademy

Introduction to Graph Databases Workshop

Graph Databases

Cypher

Filtering results

WHERE

You can filter the results of a query using the WHERE clause.

Tom Hanks movies released in 2013:

cypher
MATCH (p:Person)-[:ACTED_IN]->(m:Movie)
WHERE p.name = "Tom Hanks"
AND m.year = 2013
RETURN m.title

Comparison operators

Cypher supports operators in the WHERE clause, including:

  • Comparison operators:

    =, <> - equal, not equal

    <, > - less than, greater than

    ⇐, >= - less than or equal to, greater than or equal to

  • Strings - CONTAINS, STARTS WITH, ENDS WITH

  • Binary operators - AND, OR, XOR, NOT

  • Null values - IS NULL, IS NOT NULL

  • List membership - IN

Testing ranges

Using comparison and binary operators, you can test for ranges.

Tom Hanks movies released between 2005 and 2010:

cypher
MATCH (p:Person)-[:ACTED_IN]->(m:Movie)
WHERE p.name = "Tom Hanks"
  AND 2005 <= m.year <= 2010
RETURN m.title, m.released

String operators

There are specific operators for strings, allowing you to filter based on the contents of a string.

Movies staring someone with "Robert" in their name:

cypher
MATCH (p:Person)-[:ACTED_IN]->(m:Movie)
WHERE p.name CONTAINS "Robert"
RETURN p.name, m.title

String operators

You can also use STARTS WITH and ENDS WITH.

Movies staring someone called "Robert":

cypher
MATCH (p:Person)-[:ACTED_IN]->(m:Movie)
WHERE p.name STARTS WITH "Robert"
RETURN p.name, m.title

Null values

Properties that are not set are null in Neo4j. You can IS NULL and IS NOT NULL to filter based on null values.

This query finds people who are over 100 years old and still alive:

cypher
MATCH (p:Person)
WHERE p.died IS NULL
AND p.born.year <= 1925
RETURN p.name, p.born, p.died

Lists

You can use the IN operator to test if a value is in a list.

The Movie nodes contain list of languages spoken in the movie.

Movies in French:

cypher
MATCH (m:Movie)
WHERE "French" IN m.languages
RETURN m.title

Challenges

Complete the queries to find the following data in the graph:

  1. Directors of Horror movies released in the year 2000.

    cypher
    MATCH (d:Director)-[:DIRECTED]->(m:Movie)-[:IN_GENRE]->(g:Genre)
WHERE ?????? AND ??????
RETURN d.name

  2. All movies that do not have a tmdbId property (i.e. it is null).

    cypher
    MATCH (m:Movie)
WHERE ???????
RETURN m.title

  3. People born in the 1950’s (1950 - 1959).

    cypher
    MATCH (p:Person)
WHERE p.born.year ??????
RETURN p.name, p.born
Click to reveal the answers

  1. Directors of Horror movies released in the year 2000.

    cypher
    MATCH (d:Director)-[:DIRECTED]->(m:Movie)-[:IN_GENRE]->(g:Genre)
WHERE m.year = 2000 AND g.name = "Horror"
RETURN d.name

  2. Movies that do not have a tmdbId property (i.e. it is null).

    cypher
    MATCH (m:Movie)
WHERE m.tmdbId IS NULL
RETURN m.title

  3. People born in the 1950’s (1950 - 1959).

    cypher
    MATCH (p:Person)
WHERE 1950 <= p.born.year <= 1959
RETURN p.name, p.born

Summary

In this lesson, you learned how to filter results using the WHERE clause.