Difference between revisions of "Space Race/Relationships Tutorial"

Latest revision as of 08:43, 9 December 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. 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

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(: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, 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;

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);

Acknowledgements

NoSQLZoo is made possible by the following open-source technologies:

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@@ Line 1: / Line 1: @@
-<p>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.</p>
+<p>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.</p>
 <p>All relationships in Neo4j are directional, that is they have a start and end node. They can only possess a single <code>TYPE</code>, rather than multiple labels, but they can also possess properties similar to nodes</p>
@@ Line 6: / Line 6: @@
 [http://nosqlzoo.net/mw/visproject/visualisation.php Click here for 3d graph visualisation]
 ==Relationship types==
@@ Line 11: / Line 12: @@
    <p>The <code>Type()</code> function can return the type of a relationship</p>
    <p class='strong'>Return the type of the relationship between Astronaut and Mission</p>
-   <pre class="def"><nowiki>MATCH(n:Astronaut)-[r]->(c:Country) RETURN type(r);</nowiki>
+   <pre class="def"><nowiki>MATCH(:Astronaut)-[r]->(:Country) RETURN DISTINCT type(r);</nowiki>
 </pre>
-<pre class="ans"><nowiki>MATCH(n:Astronaut)-[r]->(m:Mission)  RETURN type(r);</nowiki>
+<pre class="ans"><nowiki>MATCH(:Astronaut)-[r]->(:Mission)  RETURN DISTINCT type(r);</nowiki>
 </pre>
 </div>
@@ Line 35: / Line 36: @@
 <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 class='strong'>Show the names of everyone that James Lovell flew with and the mission he flew with them on.</p>
+   <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 class="ans"><nowiki>MATCH(n:Astronaut{surname:"Lovell"})-[:CREWED]->(a:Mission)<-[:CREWED]-(m:Astronaut)  RETURN DISTINCT  m.surname, m.first_name</nowiki>
+<pre class="ans"><nowiki>MATCH(n:Astronaut{surname:"Lovell"})-[:CREWED]->(a:Mission)<-[:CREWED]-(m:Astronaut)  RETURN DISTINCT  m.surname, m.first_name;</nowiki>
 </pre>
 </div>
+==Saturn V Missions==
+<div class="q nonum" data-lang="neo4j">
+  <p>Aggregate functions can also be used on the result of relationships queries</p>
+  <p class='strong'>Show how many missions were launched on the Saturn V.</p>
+  <pre class="def"><nowiki>MATCH(n:LaunchVehicle{name:"Saturn V"})RETURN DISTINCT n; </nowiki>
+</pre>
+<pre class="ans"><nowiki>MATCH(:LaunchVehicle{name:"Saturn V"})<-[r:LAUNCHED_ON]-(:Mission) RETURN count(r);</nowiki>
+</pre>
+</div>
 {{Acknowledgements}}