Difference between revisions of "Space Race/Relationships Tutorial"
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<div class="q nonum" data-lang="neo4j"> | <div class="q nonum" data-lang="neo4j"> | ||
<p>Numerous relationships can be strung together. <code>DISTINCT</code> can be used to only display a result once if that node is linked to multiple times</p> | <p>Numerous relationships can be strung together. <code>DISTINCT</code> can be used to only display a result once if that node is linked to multiple times</p> | ||
| − | <p class='strong'>Show the names of everyone that James Lovell flew with | + | <p class='strong'>Show the names of everyone that James Lovell flew with.</p> |
<pre class="def"><nowiki>MATCH(n:Astronaut{surname:"Armstrong"})-[:CREWED]->(a:Mission)<-[:CREWED]-(m:Astronaut) RETURN DISTINCT m.surname, m.first_name </nowiki> | <pre class="def"><nowiki>MATCH(n:Astronaut{surname:"Armstrong"})-[:CREWED]->(a:Mission)<-[:CREWED]-(m:Astronaut) RETURN DISTINCT m.surname, m.first_name </nowiki> | ||
</pre> | </pre> | ||
Revision as of 09:38, 29 November 2019
Relationships are the most powerful part of graph-based databases. While some of the functionality these provide is possible under SQL using join tables for many to many relationships, certain queries can be constructed which would require many joins in SQL.
All relationships in Neo4j are directional, that is they have a start and end node. They can only possess a single TYPE, rather than multiple labels, but they can also possess properties similar to nodes
Contents
Visualisation
Click here for 3d graph visualisation
Relationship types
The Type() function can return the type of a relationship
Return the type of the relationship between Astronaut and Mission
MATCH(n:Astronaut)-[r]->(c:Country) RETURN type(r);
MATCH(n:Astronaut)-[r]->(m:Mission) RETURN type(r);
Born in Russia
The item in [] represents a relationship between nodes, in this case the relationship possessing the label "BORN_IN"
Note the (startNode)-[:LABEL_NAME]->(endNode) format. The direction the arrow points shows which node is the end point.
It is perfectly valid to express this relationship as (endNode)<-[:LABEL_NAME]-(startNode)
If you are not concerned about the direction of the relationships, you can also MATCH based on (node1)-[:LABEL_NAME]-(node2)
Show the Surnames of Astronauts born in Russia, and the full name of Russia rather than the USA. Hint: Use the ISO 3166-1 Alpha-2 code in all caps
MATCH(n:Astronaut)-[:BORN_IN]->(c:Country) WHERE c.abbrev ='USA' RETURN n.surname, c.name;
MATCH(n:Astronaut)-[:BORN_IN]->(c:Country) WHERE c.abbrev= 'RU' RETURN n.surname, c.name;
Flight Colleagues
Numerous relationships can be strung together. DISTINCT can be used to only display a result once if that node is linked to multiple times
Show the names of everyone that James Lovell flew with.
MATCH(n:Astronaut{surname:"Armstrong"})-[:CREWED]->(a:Mission)<-[:CREWED]-(m:Astronaut) RETURN DISTINCT m.surname, m.first_name
MATCH(n:Astronaut{surname:"Lovell"})-[:CREWED]->(a:Mission)<-[:CREWED]-(m:Astronaut) RETURN DISTINCT m.surname, m.first_name
Acknowledgements
NoSQLZoo is made possible by the following open-source technologies: