Cypher语法基础 #

Cypher特点：
├── 声明式语法：描述"要什么"而非"怎么做"
├── 模式匹配：直观表达图结构
├── ASCII艺术：用图形符号表示节点和关系
└── SQL类似：熟悉SQL的开发者容易上手

标准查询顺序：
├── MATCH / MERGE
├── OPTIONAL MATCH
├── WHERE
├── WITH
├── ORDER BY
├── SKIP / LIMIT
└── RETURN

()
(:Label)
(:Label {property: value})
(variable:Label {property: value})

MATCH ()
RETURN ()

MATCH (:Person)
RETURN *

MATCH (p:Person)
RETURN p

MATCH (p:Person {name: 'Tom'})
RETURN p

CREATE (n:Person:Actor:Director {name: 'Tom'})

--
--> 
<--
-[]->
-[:TYPE]->
-[:TYPE {property: value}]->
-[r:TYPE]->
-[r:TYPE*1..3]->

MATCH ()-->()
RETURN *

MATCH ()-[:KNOWS]-()
RETURN *

MATCH ()-[:KNOWS]->()
RETURN *

MATCH ()<-[:KNOWS]-()
RETURN *

MATCH (a)-[r:KNOWS]->(b)
RETURN a, r, b

MATCH (a)-[r:KNOWS {since: 2020}]->(b)
RETURN a, r, b

MATCH (a)-[:KNOWS]-(b)
RETURN a, b

MATCH (p:Person)-[:KNOWS]->(f:Person)
RETURN p, f

MATCH (a)-[:KNOWS]->(b)-[:KNOWS]->(c)
RETURN a, b, c

MATCH (a)-[:KNOWS]->(b)-[:WORKS_AT]->(c:Company)<-[:WORKS_AT]-(d:Person)
RETURN a, b, c, d

MATCH p = (a)-[:KNOWS*1..3]->(b)
RETURN p

命名规则：
├── 以字母开头
├── 可包含字母、数字、下划线
├── 区分大小写
└── 不能使用保留字

MATCH (person:Person)
MATCH (p1:Person)
MATCH (person_name:Person)
MATCH (Person:Person)

MATCH (1person:Person)
MATCH (my-var:Person)
MATCH (match:Person)

MATCH (`1person`:Person)
MATCH (`my-var`:Person)
MATCH (`MATCH`:Person)

MATCH (n:Person)
WHERE n.age > 18
RETURN n

MATCH (n:Person)
WHERE n.age > 18
RETURN n

MATCH (n:Person) -- 查找所有Person节点
WHERE n.age > 18 -- 筛选成年人
RETURN n -- 返回结果

MATCH (n:Person)
RETURN n.name, n.age

MATCH (n:Person)
RETURN n['name'], n['age']

MATCH (n:Person)
WITH n, 'name' AS prop
RETURN n[prop]

MATCH (n:Person)
RETURN 
  n.name,
  CASE n.status
    WHEN 'active' THEN '活跃'
    WHEN 'inactive' THEN '不活跃'
    ELSE '未知'
  END AS status_text

MATCH (n:Person)
RETURN 
  n.name,
  CASE 
    WHEN n.age < 18 THEN '未成年'
    WHEN n.age < 60 THEN '成年'
    ELSE '老年'
  END AS age_group

MATCH (n:Person)
WITH n.name AS name, n.age AS age
WHERE age > 18
RETURN name, age

MATCH (n:Person)-[:KNOWS]->(f:Person)
WITH n, count(f) AS friend_count
WHERE friend_count > 5
RETURN n.name, friend_count

MATCH (n:Person)
WITH n.name AS name
ORDER BY name
LIMIT 10
RETURN collect(name) AS names

UNWIND [1, 2, 3] AS x
RETURN x

UNWIND ['Tom', 'Jerry', 'Mike'] AS name
CREATE (p:Person {name: name})

:param names => ['Tom', 'Jerry', 'Mike']
UNWIND $names AS name
CREATE (p:Person {name: name})

MATCH (n:Person)
RETURN n

MATCH (n:Person)
RETURN n.name, n.age

MATCH (n:Person)
RETURN n.name AS name, n.age AS age

MATCH (n:Person)
RETURN n.name, n.age * 2 AS double_age

MATCH (n:Person)
RETURN DISTINCT n.name

MATCH (n:Person)
RETURN n.name, n.age
ORDER BY n.age ASC

MATCH (n:Person)
RETURN n.name, n.age
ORDER BY n.age DESC

MATCH (n:Person)
RETURN n.name, n.age
ORDER BY n.age DESC, n.name ASC

MATCH (n:Person)
RETURN n.name, n.age
ORDER BY n.age ASC NULLS FIRST

MATCH (n:Person)
RETURN n.name, n.age
ORDER BY n.age DESC NULLS LAST

MATCH (n:Person)
RETURN n
LIMIT 10

MATCH (n:Person)
RETURN n
SKIP 10
LIMIT 10

MATCH (n:Person)
RETURN n
ORDER BY n.name
SKIP 20
LIMIT 10

:param name => 'Tom'
MATCH (n:Person {name: $name})
RETURN n

:param minAge => 18
:param maxAge => 60
MATCH (n:Person)
WHERE n.age >= $minAge AND n.age <= $maxAge
RETURN n

:param names => ['Tom', 'Jerry', 'Mike']
MATCH (n:Person)
WHERE n.name IN $names
RETURN n

MATCH (a:Person {name: 'Tom'})
MATCH (b:Person {name: 'Jerry'})
CREATE (a)-[:KNOWS]->(b)

MATCH (n:Person)
RETURN n.name AS name
UNION
MATCH (n:Company)
RETURN n.name AS name

MATCH (n:Person)
RETURN n.name AS name
UNION ALL
MATCH (n:Company)
RETURN n.name AS name

建议：
├── 使用大驼峰命名：Person, Company, Product
├── 使用名词：User, Order, Item
└── 避免使用动词：Created, Has

建议：
├── 使用大写蛇形命名：KNOWS, WORKS_AT, FRIEND_OF
├── 使用动词或动词短语：ACTED_IN, DIRECTED_BY
└── 方向性明确：PARENT_OF, CHILD_OF

建议：
├── 使用小驼峰命名：firstName, lastName
├── 或使用小写蛇形命名：first_name, last_name
└── 保持一致性