Queries -- Asking Questions About Your Network

The Analogy

Imagine you could talk to your whiteboard and ask it questions in English: - "Show me all the Students" - "Who does Alice know?" - "Find everyone Alice knows through Bob"

Real graph databases use a language called Cypher for exactly this. It's like SQL (the language for regular databases) but designed for graphs. Our version is simplified but follows the same ideas!

The Query Language

Our queries follow this pattern:

MATCH (variable:Label)-[:RELATIONSHIP]->(other_variable) WHERE conditions RETURN result

Let's break that down: - MATCH = "Find me..." - (n:Person) = "...a node labeled Person (call it n)..." - -[:KNOWS]-> = "...connected by a KNOWS relationship to..." - (m) = "...another node (call it m)..." - WHERE n.name = "Alice" = "...but only where n's name is Alice..." - RETURN m = "...and give me back m"

Code Examples

from pygraphdb import Graph, execute_query

g = Graph()
g.add_node("1", label="Person", properties={"name": "Alice"})
g.add_node("2", label="Person", properties={"name": "Bob"})
g.add_node("3", label="Person", properties={"name": "Charlie"})
g.add_edge("e1", "1", "2", rel_type="KNOWS")
g.add_edge("e2", "1", "3", rel_type="KNOWS")

# Find all people
everyone = execute_query(g, "MATCH (n:Person) RETURN n")

# Find Alice specifically
alice = execute_query(g, 'MATCH (n:Person) WHERE n.name = "Alice" RETURN n')

# Find everyone Alice knows
alice_friends = execute_query(g, 'MATCH (n:Person)-[:KNOWS]->(m) WHERE n.name = "Alice" RETURN m')

Query Parts Cheat Sheet

Part	Meaning	Example
MATCH	Start searching	MATCH (n:Person)
(n:Label)	A node with a label	(p:Student)
-[:TYPE]->	A directed relationship	-[:KNOWS]->
WHERE	Filter condition	WHERE n.age = "13"
RETURN	What to give back	RETURN n