Knowledge graph queries use Cypher language, which is expressive and efficient, playing a role in graph databases equivalent to SQL in relational databases.

Basic syntax:

• MATCH is used to query nodes, relationships and properties, similar to SELECT in SQL.
• RETURN outputs search results after MATCH query, therefore MATCH must be used with RETURN.

• WHERE clause filters query results
• WHERE can combine functions exists(), string matching starts with/ends with/contains, logical operators in/not/and/or, and regular expressions for precise queries
• LIMIT clause restricts the number of returned results

Query Command	Cypher Syntax	Example
Find specified entity type	match (n:entity type) return n	match(n:River) return n
Find entities with specific properties	match (n:entity type{property:'value'}) return n	match (n:River{name:'Daduo River'}) return n
Find specific relationships	match p = (n)-[r]->(m) return p	match p = (n)-[r:Contains]->(m) return p

In graph data, deeper relationship-based queries are often required. Common association queries:

No.	Cypher Statement	Description
1	MATCH p=(n:River{name:'Daduo River'})-[r]-() RETURN p	Query all relations of Daduo River (no direction)
2	MATCH p=(n:River{name:'Daduo River'})-[r:FlowThrough]->() RETURN p	Query flow-through relationships of Daduo River (with direction)
3	MATCH p=(n)-[r:FlowThrough]->(m:Region{name:'Yaan'}) RETURN p 或 MATCH p=(n)-[r:FlowThrough]->(m:Region)where m.name='Yaan' return n.name	Find all rivers flowing through Yaan region
4	MATCH p=(n)-[r:FlowThrough]->(m)where m.name in ['Luding County','Danba County'] return n.name	Find rivers flowing through both Luding and Danba counties
4	MATCH p=(n:PowerStation{name:'Pubugou Station'})-[:LocatedIn]->(m)-[:FlowThrough]->(e) RETURN e	Find regions through which the river containing Pubugou Power Station flows

When spatial entities are stored in YuKon database, server-side spatial query is supported.

Common spatial functions:

Function	Description
st_Equals	Equal
st_Intersects	Intersect
st_Contains	Contain
st_Crosses	Cross
st_Within	Within
st_Touches	Adjacent
st_Overlaps	Overlap
st_Disjoint	Disjoint
st_Distance	Calculate distance

Query examples:

No.	Cypher Statement	Description
1	match (n:County), (m:Province{name:'Sichuan'}) where st_Contains(m.geom::geometry, n.geom::geometry) return n."name";	Find county entities within Sichuan Province (geometry type)
2	match (n:County{name:'Shuangliu'}), (m:County{name:'Chaoyang'}) return st_Distance(n.geom, m.geom);	Return distance between Shuangliu and Chaoyang (geography type)