图数据库之Cypher语⾔
1、什么是Cypher
2、写（create、merge、set、delete、remove、foreach、import）
3、读（match、optional match、where、start、聚合）
4、常规（return、order by、limit、skip、with、unwind、union）
5、函数（谓词、标准函数、集合函数、数学函数、字符串函数）
6、模式（索引、约束、统计）
1、什么是Cypher
Cypher是⼀种声明式图查询语⾔，表达⾼效查询和更新图数据库。Cypher是相对简单的查询语法，它让我们更关注业务领域问题。
2、写
Create：
创建单个节点（注意有个空格）：create (n)
创建带标签的节点（ID:n，label:Person）：create (n:Person)
创建带两个标签的节点：create (n:Person:Student)
创建带标签、属性的节点： create (n:Person {name:"weiw",age:23})
返回创建的节点：create (a {name:"Tom"}) return a
创建关系（两个节点之间的关系）：
match (a:Person),(b:Person) where a.name="zhangs" and b.name="lisi"  create (a)-[r:RELTYPE]->(b) return r
创建关系的同时设置属性：
match (a:Person),(b:Person) where a.name="zhangs" and b.name="lisi"
create (a)-[r:RELTYPE {name:a.name +"<->" + b.name}]->(b) return r
完整创建：三个节点两个关系
create p=(an {name:"an"})-[:WORKS_AT]->(neo)<-[:WORKS_AT]-(mach {name:"mach"}) return p;
Merge：
对不存在的节点创建，存在的节点返回。
merge (robert:Critic) return robert,labels(robert);
单个属性节点：merge (charlie {name:"Charlie",age:10}) return charlie;
带标签和属性的单个节点：merge (michel:Person {name:"michelDoug"}) return michel;
如果要创建节点就设置属性：merge on create
merge (keanu:Person {name:"Keanu"}) on create  ated=timestamp() return keanu;
merge函数如果到节点就设置属性：merge on match
merge (person:Person) on  match set person.found=true return person;
如果到就设置属性，没到创建节点并设置属性：merge on create on match:
merge (keanu:Person {name:"Keanu"}) on create ated=timestamp() on match set keanu.lastSeen=timestamp() return keanu; merge on match 多个属性，如果没有属性则创建：
merge (person:Person) on match set person.found=true,person.lastAccessed=timestamp() return person;
merge 关系：
match (charlie:Person {name:"Charlie"}),(wall:Movie {title:"Wall"})
merge (charlie)-[r:ACTED_AT]->(wall)  return r;
merge多重关系：
MATCH (oliver:Person { name:'Oliver Stone' }),(reiner:Person { name:'Rob Reiner' })
MERGE (oliver)-[:DIRECTED]->(movie:Movie)<-[:ACTED_IN]-(reiner) RETURN movie
merge⾮直接关系：
MATCH (charlie:Person { name:'Charlie Sheen' }),(oliver:Person { name:'Oliver Stone' })
MERGE (charlie)-[r:KNOWS]-(oliver) RETURN r
merge 上使⽤唯⼀性约束：
CREATE CONSTRAINT ON (n:Person) ASSERT n.name IS UNIQUE;
CREATE CONSTRAINT ON (n:Person) le IS UNIQUE;
MERGE (laurence:Person { name: 'Laurence Fishburne' }) RETURN laurence ；
Set:
⽤于更新⼀个节点和关系的标签或属性。
create (n { name: 'Andres' }) ;
MATCH (n { name: 'Andres' }) SET n.surname = 'Taylor' RETURN n;
删除属性：MATCH (n { name: 'Andres' })  SET n.name = NULL RETURN n
在节点和关系之间复制属性：MATCH (at { name: 'Andres' }),(pn { name: 'Peter' }) SET at = pn RETURN at, pn;
从map添加属性：MATCH (peter { name: 'Peter' }) SET peter += { hungry: TRUE , position: 'Entrepreneur' }
设置多个属性：MATCH (n { name: 'Andres' }) SET n.position = 'Developer', n.surname = 'Taylor'
在节点上加标签：    MATCH (n { name: 'Stefan' }) SET n :German RETURN n
MATCH (n { name: 'Emil' }) SET n :Swedish:Bossman RETURN n
DELETE：
删除节点和关系
删除单个节点：MATCH (n:Useless) DELETE n;
删除节点和连接它的关系：MATCH (n { name: 'Andres' })-[r]-() DELETE n, r
删除所有节点和关系：MATCH (n) OPTIONAL MATCH (n)-[r]-() DELETE n,r
REMOVE：
删除标签和属性
删除属性：MATCH (andres { name: 'Andres' }) REMOVE andres.age RETURN andres;
删除节点的标签：MATCH (n { name: 'Peter' }) REMOVE n:German RETURN n;
删除多重标签：MATCH (n { name: 'Peter' }) REMOVE n:German:Swedish RETURN n
FOREACH:
为所有节点设置mark属性：MATCH p =(begin)-[*]->(END ) WHERE begin.name='A' AND END .name='D' FOREACH (n IN nodes(p)| SET n.marked = TRUE )
CREATE UNIQUE:
创建唯⼀性节点：MATCH (root { name: 'root' }) CREATE UNIQUE (root)-[:LOVES]-(someone) RETURN someone
IMPORT CSV:
LOAD CSV WITH HEADERS FROM "neo4j/docs/2.2.3/csv/import/persons.csv" AS csvLine CREATE (p:Person { id:
toInt(csvLine.id), name: csvLine.name })
id,name
1,Charlie Sheen
2,Oliver Stone
3,Michael Douglas
4,Martin Sheen
5,Morgan Freeman
3、读
MATCH:
查询所有节点：MATCH (n) RETURN n
查询指定标签的节点：MATCH (movie:Movie) RETURN movie;
关联节点：MATCH (director { name:'Oliver Stone' })--(movie) RETURN movie.title
查询标签：MATCH (charlie:Person { name:'Charlie Sheen' })--(movie:Movie) RETURN movie
关系查询：MATCH (martin { name:'Martin Sheen' })-->(movie) RETURN movie.title
MATCH (martin { name:'Martin Sheen' })-[r]->(movie) RETURN r
通过关系类型查询：MATCH (wallstreet { title:'Wall Street' })<-[:ACTED_IN]-(actor) RETURN actor
OPTIONAL MATCH:
与match类似，只是如果没有匹配上，则将使⽤null作为没有匹配上的模式。类似于SQL中的外连接。
匹配关系：match (a:Movie {title:"Wall Street"}) optional match (a)-->(x) return x;  如果没有返回null。
匹配属性：match (a:Movie {title:"Wall Street"}) optional match (a)-->(x) return x,x.name
WHERE:
MATCH (n)  WHERE n.name = 'Peter' XOR (n.age < 30 AND n.name = "Tobias") OR NOT (n.name = "Tobias" OR n.name="Peter") RETURN n;
过滤标签：MATCH (n)  WHERE n:Swedish  RETURN n;
过滤属性：MATCH (n)  WHERE n.age < 30  RETURN n;
MATCH (n)  WHERE HAS (n.belt)  RETURN n;
正则：MATCH (n)  WHERE n.name =~ 'Tob.*'  RETURN n;
在where中使⽤pattern：
MATCH (tobias { name: 'Tobias' }),(others)  WHERE others.name IN ['Andres', 'Peter'] AND (tobias)<--(others)  RETURN others
使⽤not：MATCH (persons),(peter { name: 'Peter' })  WHERE NOT (persons)-->(peter)  RETURN persons
使⽤属性：MATCH (n)  WHERE (n)-[:KNOWS]-({ name:'Tobias' })  RETURN n
关系类型：MATCH (n)-[r]->()  WHERE n.name='Andres' AND type(r)=~ 'K.*'  RETURN r
使⽤IN：MATCH (a)  WHERE a.name IN ["Peter", "Tobias"]  RETURN a
MATCH (n)  WHERE n.belt = 'white'  RETURN n
MATCH (n)  WHERE n.belt = 'white' OR n.belt IS NULL RETURN n  ORDER BY n.name
过滤NULL：MATCH (person)  WHERE person.name = 'Peter' AND person.belt IS NULL RETURN person
START：
START n=node:nodes(name = "A")  RETURN n
START r=relationship:rels(name = "Andrés")  RETURN r
START n=node:nodes("name:A")  RETURN n
聚合函数：
count：MATCH (n { name: 'A' })-->(x)  RETURN n, count(*)
sum：MATCH (n:Person)  RETURN sum(n.property)
avg：MATCH (n:Person)  RETURN avg(n.property)
percentileDisc：计算百分位。MATCH (n:Person)  RETURN percentileDisc(n.property, 0.5) percentileCont：MATCH (n:Person)  RETURN percentileCont(n.property, 0.4)
stdev：计算标准偏差。MATCH (n)  WHERE n.name IN ['A', 'B', 'C'] RETURN stdev(n.property) stdevp：MATCH (n) WHERE n.name IN ['A', 'B', 'C']  RETURN stdevp(n.property)
max：MATCH (n:Person) RETURN max(n.property)
min：MATCH (n:Person)  RETURN min(n.property)
collect：MATCH (n:Person) RETURN collect(n.property)
distinct：MATCH (a:Person { name: 'A' })-->(b) RETURN count(s)
4、常规
RETURN:
返回⼀个节点：match (n {name:"B"}) return n;
返回⼀个关系：match (n {name:"A"})-[r:KNOWS]->(c) return r;
返回⼀个属性：match (n {name:"A"}) return n.name;
返回所有节点：match p=(a {name:"A"})-[r]->(b) return *;
列别名： match (a {name:"A"}) return a.age as thisisage;
表达式： match (a {name:"A"}) return a.age >30 ,"literal",(a)-->();
唯⼀结果：match (a {name:"A"})-->(b) return distinct b;
ORDER BY:
通过属性排序所有节点：match (n) return n order by n.name;
多个属性排序：match (n) return n order n.name,n.age;
指定排序⽅式：match (n) return n order by n.name desc;
NULL值的排序：match (n) return n.length,n order by n.length;
LIMIT:
match (n) return n order by n.name limit 3;
SKIP:
match (n) return n order by n.name skip 3;
match (n) return n order by n.name skip 1 limit 3;
WITH:
过滤聚合函数的结果：
MATCH (david { name: "David" })--(otherPerson)-->()  WITH otherPerson, count(*) AS foaf
WHERE foaf > 1  RETURN otherPerson;
collect前排序结果：MATCH (n)  WITH n  ORDER BY n.name DESC LIMIT 3  RETURN collect(n.name; limit搜索路径的分⽀：
MATCH (n { name: "Anders" })--(m)  WITH m
ORDER BY m.name DESC LIMIT 1  MATCH (m)--(o)  RETURN o.name;
UNWIND:
将⼀个集合展开为⼀个序列：unwind[1,2,3] as x return x;
创建⼀个去重的集合：with [1,1,2,3] as coll unwind coll x with distinct x return collect(x) as set;
UNION & UNION ALL:
不删除重复：match (n:Actor) return n.name as name union all match(n:Movie) return b.title as name;
删除重复：match (n:Actor) return n.name as name union match(n:Movie) return b.title as name;
5、函数
谓词：
ALL：ALL(identifier in collection WHERE predicate)
ANY：ANY(identifier in collection WHERE predicate)
MATCH (a)  WHERE a.name='Eskil' AND ANY (x IN a.array WHERE x = "one")  RETURN a NONE：NONE(identifier in collection WHERE predicate)
SINGLE：SINGLE(identifier in collection WHERE predicate)
EXISTS：EXISTS( pattern-or-property )
MATCH (n)
WHERE EXISTS(n.name)
RETURN n.name AS name, EXISTS((n)-[:MARRIED]->()) AS is_married
Scalar function：
length：返回集合长度。match p=(a)-->(b)-->(c) where a.name="Alice" return length(p)
type：关系类型。match (n)-[r]->() where n.name='Alice' return type(r)
id：返回节点或关系的id。match (a) return id(a)
coalesce：返回第⼀个not null值。match (a) where a.name='Alice' return coalesce(a.s)
head：返回集合的第⼀个元素。match (a) where a.name='Alic' return a.array,head(a.array);
last：返回集合的最后⼀个元素。match (a) where a.name='Alic' return a.array,last(a.array);
timestamp：返回当前时间的毫秒
startNode：返回⼀个关系的开始节点。match (x:foo)-[r]-() return startNode(r);
endNode：返回⼀个关系的结束节点。match (x:foo)-[r]-() return endNode(r);
toInt,toFloat,toString
集合函数：
nodes(path)：返回path中节点。match p=(a)-->(b)-->(c) where a.name='Alice' and c.name='Eskil' return nodes(p) relationships(path)：返回path中的关系。match p=(a)-->(b)-->(c) where a.name='Alice' and c.name='Eskil' return relationships(p) labels：返回节点标签。match (a) where a.name='Alice' return labels(a);
keys：返回节点的所有属性。match (a) where a.name='Alice' return keys(a);
extract：从⼀个节点或关系集合中返回单个属性或值的集合。EXTRACT( identifier in collection | expression )
MATCH p=(a)-->(b)-->(c)
WHERE a.name='Alice' AND b.name='Bob' AND c.name='Daniel'
RETURN extract(n IN nodes(p)| n.age) AS extracted
filter：FILTER(identifier in collection WHERE predicate)
tail：返回集合中的⾮第⼀个元素的集合。
range：RANGE( start, end [, step] ) 。RETURN range(0,10), range(2,18,3)
reduce：REDUCE( accumulator = initial, identifier in collection | expression )。将满⾜条件的节点的age属性值求和。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
数学函数：
abs()，acos()，asin()，atan()，atan2(x,y)，cos()，cot()，degree()，e()返回⼀个常量，exp(2) e的⼆次⽅，floor(0.9)=0.0，haversin()，log()，log10()，pi()常量PI，radians(180)，rand()返回0到1.0的值，round(3.14)=3.0，sign()，sin()，sqrt()，tan()
字符串函数：
str(1)="1"，replace("hello",'l','w')=hewwo，substring('hello',1,3)="ell"，substring("hello",2)="llo"，left("hello",3)="hel"，
right("hello",3)="llo"，ltrim("    hello")="hello"，rtrim("hello  ")="hello"，trim("  hello  ")="hello"，lower("HELLO")="hello"，upper("hello")="HELLO"，split("one,two",",")=["one","two"]
6、模式（索引、约束、统计）
索引：
标签上创建索引：create index on :Person(name)
drop index on :Person(name)
约束：
创建唯⼀约束：CREATE CONSTRAINT ON (book:Book) ASSERT book.isbn IS UNIQUE
删除约束：DROP CONSTRAINT ON (book:Book) ASSERT book.isbn IS UNIQUE

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