Nosql-neo4j-Cypher 语句（3）

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//不常见字符，使用反引号 MATCH (`This isn\'t a common variable`) WHERE `This isn\'t a common variable`.name = 'A' RETURN `This isn\'t a common variable`.happy // 使用别名 MATCH (a { name: 'A' }) RETURN a.age AS SomethingTotallyDifferent //其他形式的表达式 MATCH (a { name: 'A' }) RETURN a.age > 30, "I'm a literal",(a)-->() // 去重 MATCH (a { name: 'A' })-->(b) RETURN DISTINCT b

WITH语句允许查询链接在一起，一个查询的结果作为另一个查询的输入 WITH变量范围是WITH下面的语句

使用WITH和 group by and LIMIT 限制下一部分的输入数量
和WHERE结合使用过滤聚合值
使用WITH进行读写分析，读的部分只读，写的部分只写

//过滤聚合值，读 WITH 聚合 WHERE
//返回和David联系的至少一次外连接的人
MATCH (david { name: 'David' })--(otherPerson)-->()
WITH otherPerson, count(*) AS foaf
WHERE foaf > 1
RETURN otherPerson.name
//在collect之前对数据进行排序和限制
// 先读，WITH，排序
MATCH (n)
WITH n
ORDER BY n.name DESC LIMIT 3
RETURN collect(n.name)
//限制下一部分的搜索范围
MATCH (n { name: 'Anders' })--(m)
WITH m
ORDER BY m.name DESC LIMIT 1
MATCH (m)--(o)
RETURN o.name
UNWIND
UNWIND解开List成为一行

这个list可能是collect处理的
UNWIND [1, 2, 3, NULL ] AS x
RETURN x, 'val' AS y
WITH [1, 1, 2, 2] AS coll
UNWIND coll AS x
WITH DISTINCT x
RETURN collect(x) AS setOfVals
// 展开任何返回list的表达式
WITH [1, 2] AS a,[3, 4] AS b
UNWIND (a + b) AS x
RETURN x
// 展开list的list
WITH [[1, 2],[3, 4], 5] AS nested
UNWIND nested AS x
UNWIND x AS y
RETURN y
//应用空list，返回空
UNWIND [] AS empty
RETURN empty, 'literal_that_is_not_returned'
// 为了不处理空list，使用CASE
WITH [] AS list
UNWIND
      WHEN list = []
         THEN [null]
      ELSE list
   END AS emptylist
RETURN emptylist
UNWIND NULL AS x
RETURN x, 'some_literal'
// 通过参数创建节点
  "events" : [ {
    "year" : 2014,
    "id" : 1
    "year" : 2014,
    "id" : 2
UNWIND $events AS event
MERGE (y:Year { year: event.year })
MERGE (y)<-[:IN]-(e:Event { id: event.id })
RETURN e.id AS x
ORDER BY x
WHERE
WHERE是MATCH, OPTIONAL MATCH and WITH语句的一部分
WHERE变量使用index可以提高查询性能
以下面graph为例：

// 创建节点
CREATE (andy:Swedish:Person {name: 'Andy',belt:'white',age:36}) 
CREATE (peter:Person {name: 'Peter',email:'[email protected]',age:35}) 
CREATE (timothy:Person {name: 'Timothy',address:'Sweden/Malmo',age:25}) 
CREATE (fido:Dog {name: 'Fido'}) 
CREATE (ozzy:Dog {name: 'Ozzy'}) 
CREATE (andy_dog:Dog {name: 'Andy'}) 
CREATE (banana:Toy {name: 'Banana'}) 
// 创建节关系
CREATE (andy)-[:HAS_DOG{since:2016}]->(andy_dog)
CREATE (andy)-[:KNOWS{since:1999}]->(peter)
CREATE (andy)-[:KNOWS{since:2012}]->(timothy)
CREATE (peter)-[:HAS_DOG{since:2010}]->(fido)
CREATE (peter)-[:HAS_DOG{since:2018}]->(ozzy)
CREATE (fido)-[:HAS_TOP]->(banana)
//AND, OR, XOR and NOT
MATCH (n:Person)
WHERE n.name = 'Peter' XOR (n.age < 30 AND n.name = 'Timothy') OR NOT (n.name = 'Timothy' OR n.name = 'Peter')
RETURN n.name, n.age
//过滤节点标签
MATCH (n)
WHERE n:Swedish
RETURN n.name, n.age
//过滤节点属性
MATCH (n:Person)
WHERE n.age < 30
RETURN n.name, n.age
//过滤关系属性
MATCH (n:Person)-[k:KNOWS]->(f)
WHERE k.since < 2000
RETURN f.name, f.age, f.email
//动态计算属性
WITH 'AGE' AS propname
MATCH (n:Person)
WHERE n[toLower(propname)]< 30
RETURN n.name, n.age
//属性是否存在
MATCH (n:Person)
WHERE EXISTS (n.belt)
RETURN n.name, n.belt
字符串匹配
STARTS WITH and ENDS WITH  and ONTAINS，大小写敏感
// STARTS WITH
MATCH (n:Person)
WHERE n.name STARTS WITH 'Pet'
RETURN n.name, n.age
//ENDS WITH 
MATCH (n:Person)
WHERE n.name ENDS WITH 'ter'
RETURN n.name, n.age
//CONTAINS
MATCH (n:Person)
WHERE n.name CONTAINS 'ete'
RETURN n.name, n.age
MATCH (n:Person)
WHERE NOT n.name ENDS WITH 'y'
RETURN n.name, n.age
Cypher支持正则表达式，Cypher正则继承与Java的正则

支持改变字符串匹配模式：case-insensitive (?i), multiline (?m) and dotall (?s)

忽略大小写：MATCH (n) WHERE n.name =~ '(?i)Lon.*' RETURN n

使用正则表达式：=~ 'regexp'
MATCH (n:Person)
WHERE n.name =~ 'Tim.*'
RETURN n.name, n.age
//某些字符不使用正则
// . or * 使用转义字符
MATCH (n:Person)
WHERE n.email =~ '.*\\.com'
RETURN n.name, n.age, n.email
//大小写不敏感
MATCH (n:Person)
WHERE n.name =~ '(?i)AND.*'
RETURN n.name, n.age
//有外连接到timothy的人，WHERE中加入图模式
MATCH (timothy:Person { name: 'Timothy' }),(other:Person)
WHERE other.name IN ['Andy', 'Peter'] AND (timothy)<--(other)
RETURN other.name, other.age
//模式中使用NOT不匹配
MATCH (person:Person),(peter:Person { name: 'Peter' })
WHERE NOT (person)-->(peter)
RETURN person.name, person.age
//add properties to your patterns
MATCH (n:Person)
WHERE (n)-[:KNOWS]-({ name: 'Timothy' })
RETURN n.name, n.age
//过滤关系类型
MATCH (n:Person)-[r]->()
WHERE n.name='Andy' AND type(r)=~ 'K.*'
RETURN type(r), r.since
WHERE中使用子查询
子查询也可以用于指定模式是否存在

子查询使用{}
子查询可以使用外部的变量
subquery was introduced in Neo4j 4.0
语法格式：
EXISTS {
 MATCH [Pattern]
 WHERE [Expression]
//一般的子查询
MATCH (person:Person)
WHERE EXISTS {
  MATCH (person)-[:HAS_DOG]->(:Dog)
RETURN person.name as name
//子查询中加入WHERE
MATCH (person:Person)
WHERE EXISTS {
  MATCH (person)-[:HAS_DOG]->(dog :Dog)
  WHERE person.name = dog.name
RETURN person.name as name
//子查询嵌套
MATCH (person:Person)
WHERE EXISTS {
  MATCH (person)-[:HAS_DOG]->(dog:Dog)
  WHERE EXISTS {
    MATCH (dog)-[:HAS_TOY]->(toy:Toy)
    WHERE toy.name = 'Banana'
RETURN person.name as name
WHERE中使用list
//判断是否在list中
MATCH (a:Person)
WHERE a.name IN ['Peter', 'Timothy']
RETURN a.name, a.age
//却失的值为null，在判断是为false
MATCH (n:Person)
WHERE n.belt = 'white'
RETURN n.name, n.age, n.belt
//IS NULL
MATCH (n:Person)
WHERE n.belt = 'white' OR n.belt IS NULL RETURN n.name, n.age, n.belt
ORDER BY n.name
WHERE中使用范围
MATCH (a:Person)
WHERE a.name >= 'Peter'
RETURN a.name, a.age