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Cypher

Humane (optimised for reading) pattern matching query language for graphs.

http://neo4j.com/docs/stable/cypher-query-lang.html

http://neo4j.com/docs/stable/cypher-refcard/

Patterns

• Node

  • (n)

• Labels

  • (n:Label)

• Properties

  • (n {name: {value}})

• Relationships

  • directional (n)-->(m), (n)<--(m)
  • non directional (n)--(m)

Clauses

• START | RETURN
  • https://youtu.be/NeJHRpbIqV0?t=492
  • START <lookup> RETURN <expressions>
  • START binds terms with simple lookup (directly using known ids, or based on indexed Property)
  • RETURN expressions specify result set
• aggregation
  • https://youtu.be/NeJHRpbIqV0?t=570
  • in SQL (group by)
  • whenever you use grouping expressing in statement, then all the non grouped elements of the statement will be used to define the aggregation column
  • count(*) is example of aggregation statement
• MATCH
  • https://youtu.be/NeJHRpbIqV0?t=658
  • START <lookup> MATCH <pattern> RETURN <expressions>
  • describes a pattern of nodes and relationships
    • node terms in optional parenthesis
    • lines with arrows for relationships
• WHERE
  • https://youtu.be/NeJHRpbIqV0?t=747
  • very similar to SQL
  • START <lookup> [MATCH <pattern>] WHERE <condition> RETURN <expression>
  • filters nodes or relationships
    • uses expression to constrain elements
• CREATE
  • https://youtu.be/NeJHRpbIqV0?t=815
  • Cypher not just for reading, also for updating the graph
  • can create nodes and relationships
    • create nodes with optional properties
    • create relationship (must have a type)
  • CREATE UNIQUE: creates graph if not there... if it is there, leaves it untouched
  • CREATE <node> [,node or relationship] RETURN <expression>
• SET
  • https://youtu.be/NeJHRpbIqV0?t=851
  • set property or delete | update a property on node or relationship
    • must follow a start
  • SET [<node property>][<relationship property>]
• DELETE
  • https://youtu.be/NeJHRpbIqV0?t=872
  • delete a node, relationship or property
    • must follow a START
    • to delete a node, all relationships must be deleted first
      • because of graph database constraint... no broken links
  • DELETE [<node>|<relationship>|<property>]
• SKIP | LIMIT
  • https://youtu.be/NeJHRpbIqV0?t=1557
  • SKIP will skip the first n results, LIMIT will only return n results