Neo4j | Cypher 参考文档

Neo4j | Cypher 参考文档

!!!这是一篇从 neo4j 开发文档提炼出来, 原文->

Patterns and pattern-matching 是 Cypher 的精髓

1. Patterns 模式

node|label|type|property|path
- (a) 节点
- (a)–(b) 相关节点模式
- (a:LABEL1:LABEL2) 指定label模式
- (a {key:”value”}) 指定属性的模式
- (a)-[r:TYPE1|TYPE2]-(b) 指定关系类型模式
- (a)-[r*2..5]->(b) 可变长度的模式
- p = (a)-[*2..5]->(b) 指定路径的模式

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2. Clauses 停用词

基本上弄清楚每个停用词的用法, Cypher 算是入门了, 这里就不展开了

• CREATE
• MATCH
• MERGE
• WHERE
• SET, REMOVE, DELETE, DETACH DELETE, FOREACH
• WITH
• UNWIND
• RETURN
• ORDER BY
• SKIP
• LIMIT

示例:

match (neo:label) where neo.name="NEO4J" return neo order by neo.age skip 2 limit 10

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3. Operators 操作

• 属性操作: . for property access, [] for dynamic property access

• 数学操作: +, -, *, /, %, ^

• 逻辑操作: =, <>, <, >, <=, >=, IS NULL, IS NOT NULL, AND, OR, XOR, NOT

• 图操作符: STARTS WITH, ENDS WITH, CONTAINS

• 正则操作: =~ for regex matching

• 集合操作: IN to check existence of an element in a list, [] for accessing element(s)

• schedule操作: DISTINCT

• 列表遍历操作: FOREACH(item in nodes(p) | SET n.marked = TRUE)

• 索引操作: CREATE INDEX ON :Person(firstname, surname)

• 约束操作: CREATE CONSTRAINT ON (book:Book) ASSERT book.isbn IS UNIQUE

• CSV导入操作: LOAD CSV FROM ‘https://neo4j.com/docs/developer-manual/3.3/csv/artists.csv’ AS line
  CREATE (:Artist { name: line[1], year: toInteger(line[2])})

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4. Function 函数

知道什么场景下使用什么函数, 就算进阶了

4.1 Predicate functions

• all(variable IN list WHERE predicate) : list 每一个元素满足条件, 返回 true
• any(variable IN list WHERE predicate) : list 存在一个元素满足条件, 返回 true
• exists(pattern-or-property) : 存在某种”模式”, 返回 true
• single(variable IN list WHERE predicate) : list 只有一个元素满足条件, 返回 true
• none(variable IN list WHERE predicate) : list 没有一个元素满足条件, 返回 true

示例:

MATCH p =(a)-[*1..3]->(b)
WHERE a.name = 'Alice' AND b.name = 'Daniel' AND ALL (x IN nodes(p) WHERE x.age > 30)
RETURN p
All nodes in the returned paths will have an age property of at least '30'.
----------------------------------------------------
MATCH (n)
WHERE exists(n.name)
RETURN n.name AS name, exists((n)-[:MARRIED]->()) AS is_married

4.2 Scalar functions

• endNode()
• startNode()
• id()
• length()
• size()
• type()
• properties()

4.3 Aggregating functions

• avg()
• collect()
• count()
• max()
• min()
• sum()

4.4 List functions

• extract() : map 操作
• reduce() : reduce 操作
• filter() : 过滤操作
• keys() : 获取节点的属性集
• labels() : 获取节点的标签集
• nodes() : 获取路径中的节点集
• relationship() : 获取路径的关系集
• range() : 自定义列表

示例:

MATCH p =(a)-->(b)
WHERE a.name = 'Alice' AND b.name = 'Bob'
RETURN extract(n IN nodes(p)| n.age) AS extracted
-----------------------------------------
MATCH (a)
WHERE a.name = 'Eskil'
RETURN a.array, filter(x IN a.array WHERE size(x)= 3)
-------------------------------
MATCH p =(a)-->(b)-->(c)
WHERE a.name = 'Alice' AND b.name = 'Bob' AND c.name = 'Daniel'
RETURN reduce(totalAge = 0, n IN nodes(p)| totalAge + n.age) AS reduction

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5. Expression 表达规则

An expression in Cypher can be:

- A decimal (integer or double) literal: 13, -40000, 3.14, 6.022E23.
- A hexadecimal integer literal (starting with 0x): 0x13zf, 0xFC3A9, -0x66eff.
- An octal integer literal (starting with 0): 01372, 02127, -05671.
- A string literal: 'Hello', "World".
- A boolean literal: true, false, TRUE, FALSE.
- A variable: n, x, rel, myFancyVariable, `A name with weird stuff in it[]!`.
- A property: n.prop, x.prop, rel.thisProperty, myFancyVariable.`(weird property name)`.
- A dynamic property: n["prop"], rel[n.city + n.zip], map[coll[0]].
- `A parameter: $param, $0`
- A list of expressions: ['a', 'b'], [1, 2, 3], ['a', 2, n.property, $param], [ ].
- A function call: length(p), nodes(p).
- An aggregate function: avg(x.prop), count(*).
- `A path-pattern: (a)-->()<--(b).`
- An operator application: 1 + 2 and 3 < 4.
- A predicate expression is an expression that returns true or false: a.prop = 'Hello', length(p) > 10, exists(a.name).
- A regular expression: a.name =~ 'Tob.*'
- A case-sensitive string matching expression: a.surname STARTS WITH 'Sven', a.surname ENDS WITH 'son' or a.surname CONTAINS 'son'
- A CASE expression.

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6. Return 返回

return 的类型有三种 list, map, record