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Space Race/Relationships Tutorial

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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. A good example is the number of connections required to link one node to another.

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


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Relationship types

The Type() function can return the type of a relationship

Return the type of the relationship between Astronaut and Mission

MATCH(:Astronaut)-[r]->(:Country) RETURN DISTINCT type(r);
MATCH(:Astronaut)-[r]->(:Mission)  RETURN DISTINCT 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,;
MATCH(n:Astronaut)-[:BORN_IN]->(c:Country) WHERE c.abbrev= 'RU' RETURN n.surname,;

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;

Saturn V Missions

Aggregate functions can also be used on the result of relationships queries

Show how many missions were launched on the Saturn V.

MATCH(n:LaunchVehicle{name:"Saturn V"})RETURN DISTINCT n; 
MATCH(:LaunchVehicle{name:"Saturn V"})<-[r:LAUNCHED_ON]-(:Mission) RETURN count(r);


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