neo4j简介
- 开源 NoSQL 数据库，原生的图数据库，2003 年开始开发，使用 scala和java 语言，2007年开始发布；
- 世界上最先进的图数据库之一，提供原生的图数据存储，检索和处理；
- 采用属性图模型（Property graph model），极大的完善和丰富图数据模型；
- 专属查询语言 Cypher，直观，高效；
图形数据库应用场景：
- 银行欺诈
- 保险欺诈
- 电子商务欺诈
- 工商企业图谱
- 社交网络
Neo4j图数据库中基本元素与概念
- 节点（node）：一个实体记录，就像关系型数据库中的一条记录。一个节点包含多个属性和标签。
- 关系（relationship）：
- 属性（property）：由键值对组成的，就像java当中哈希，
- 标签（lable）：一组拥有相同属性的节点，但不强制要求相同，一个节点可以有多个标签。
- 路径（path）
Cypher查询语言
Cypher是一种生命是图数据库查询语言，类似关系数据库中的SQL。
- MATCH：匹配图模式
- WHERE：过滤条件
- RETURN：定义返回的结果
基本语法：
- 增（CREATE）
- 删（DELETE）
- 改（SET）
- 查（MATCH）
- 函数
- WITCH
语法：
<!-- 1. 全表扫描 -->
<!-- mysql -->
SELECT p.*
FROM products as p;
<!-- neo4j -->
MATCH (p:Product)
RETURN p;
<!-- 2. 查询价格最贵的10个商品，只返回商品名字和单价 -->
<!-- mysql -->
SELECT p.ProductName, p.UnitPrice
FROM products as p
ORDER BY p.UnitPrice DESC
LIMIT 10;
<!-- neo4j -->
MATCH (p:Product)
RETURN p.productName, p.unitPrice
ORDER BY p.unitPrice DESC
LIMIT 10;
<!-- 3. 按照商品名字筛选 -->
<!-- mysql -->
SELECT p.ProductName, p.UnitPrice
FROM products AS p
WHERE p.ProductName = 'Chocolade';
<!-- neo4j -->
MATCH (p:Product)
WHERE p.productName = "Chocolade"
RETURN p.productName, p.unitPrice;
<!-- 其他的写法 -->
MATCH (p:Product {productName:"Chocolade"})
RETURN p.productName, p.unitPrice;
<!-- 4. 按照商品名字筛选2 -->
<!-- mysql -->
SELECT p.ProductName, p.UnitPrice
FROM products as p
WHERE p.ProductName IN ('Chocolade','Chai');
<!-- neo4j -->
MATCH (p:Product)
WHERE p.productName IN ['Chocolade','Chai']
RETURN p.productName, p.unitPrice;
<!-- 5. 模糊查询和数值过滤 -->
<!-- mysql -->
SELECT p.ProductName, p.UnitPrice
FROM products AS p
WHERE p.ProductName LIKE 'C%' AND p.UnitPrice > 100;
<!-- neo4j -->
MATCH (p:Product)
WHERE p.productName STARTS WITH "C" AND p.unitPrice > 100
RETURN p.productName, p.unitPrice;
<!-- 6. 多表联合查询-->
<!-- mysql -->
SELECT DISTINCT c.CompanyName
FROM customers AS c
JOIN orders AS o ON (c.CustomerID = o.CustomerID)
JOIN order_details AS od ON (o.OrderID = od.OrderID)
JOIN products AS p ON (od.ProductID = p.ProductID)
WHERE p.ProductName = 'Chocolade';
<!-- neo4j -->
MATCH (p:Product {productName:"Chocolade"})<-[:PRODUCT]-(:Order)<-[:PURCHASED]-(c:Customer)
RETURN distinct c.companyName;
<!-- 7. 分组topN -->
<!-- mysql -->
SELECT e.EmployeeID, count(*) AS Count
FROM Employee AS e
JOIN Order AS o ON (o.EmployeeID = e.EmployeeID)
GROUP BY e.EmployeeID
ORDER BY Count DESC LIMIT 10;
<!-- neo4j -->
MATCH (:Order)<-[:SOLD]-(e:Employee)
RETURN e.name, count(*) AS cnt
ORDER BY cnt DESC LIMIT 10
1优于2
1. MATCH (n) OPTIONAL MATCH (n)-[r]->() RETURN count(n.prop) + count(r.prop);
2. MATCH (n) OPTIONAL MATCH (n)-[r]->() RETURN count(*) + count(*);
//增
create (:pig{name:"猪爷爷",age:15});
create (:pig{name:"猪爷爷",age:13});
//查
match (a:pig{name:"猪奶奶"}) match (b:pig{name:"猪爷爷"}) create (a)-[r:夫妻]->(b) return r;
create (:pig{name:"猪爸爸",age:12})-[:夫妻{age:5}]->(:pig{name:"猪妈妈",age:9});
create (:pig{name:"佩奇",age:2})-[:姐弟]->(:pig{name:"乔治",age:1});
match (a:pig{name:"猪爸爸"}) match (b:pig{name:"猪爷爷"}) create (b)-[r:父子]->(a) return r;
match (a:pig{name:"猪爸爸"}) match (b:pig{name:"佩奇"}) create (b)-[r:父女]->(a) return r;
match (a:pig{name:"猪爷爷"}) match (b:pig{name:"佩奇"}) create (b)-[r:孙女]->(a) return r;
match (a:pig{name:"猪奶奶"}) match (b:pig{name:"佩奇"}) create (b)-[r:孙女]->(a) return r;
match (a:pig{name:"猪奶奶"}) match (b:pig{name:"猪爸爸"}) create (b)-[r:母女]->(a) return r;
//改
match (n:pig{name:"猪妈妈"}) set n.age=8
create (:die:pig{name:"猪祖父",age:20}),(:pig{name:"猪祖奶",age:21});
//删
match (n:die) delete n;
match p=allshortestpath((:Star{name:"小明"})-[*..5]->(:Star{name:"王大拿"})) return p;
match (:Star{name:"王大拿"})->() limit 50;
csv数据导入
LOAD CSV WITH HEADERS FROM ’file:///data/locations.csv’ AS line
WITH split(line.locations,";") as locations, line.title as title
UNWIND locations AS location --类似for location in locations
MERGE (x:Location {name:location})
MERGE (m:Movie {title:title})
MERGE (m)-[:FILMED_IN]->(x)
neo4j下载及安装
Download Neo4j 安装在下载成功跳转页下拉内容中有写，需复制“Activation Key”中激活码进行激活
NEO4J安装教程 windows下安装neo4j报错解决 jdk下载地址
Invoke-Neo4j : Cannot validate argument on parameter 'ArgumentList'. The argument is null, empty, or an element of the argument collection contains a null value. Supply a collection that does not contain any null values and then try the command again.
NEO4J_HOME = D: eo4j-community-4.2.4
path > ;%NEO4J_HOME%in;
（1）neo4j browser
（2）neo4j bloom
python 连接 neo4j
# pip3 install neo4j-driver
# python3 example.py
from neo4j import GraphDatabase, basic_auth
driver = GraphDatabase.driver(
"bolt://<HOST>:<BOLTPORT>",
auth=basic_auth("<USERNAME>", "<PASSWORD>"))
cypher_query = '''
MATCH (m:Movie {title:$movie})<-[:RATED]-(u:User)-[:RATED]->(rec:Movie)
RETURN distinct rec.title AS recommendation LIMIT 20
'''
with driver.session(database="neo4j") as session:
results = session.read_transaction(
lambda tx: tx.run(cypher_query,
movie="Crimson Tide").data())
for record in results:
print(record['recommendation'])
driver.close()
参考资料：
NoSQL 新贵之崛起的 Neo4j 受益匪浅
知识图谱和 Neo4j 浅析 知识图谱使用场景及neo4j性能方面的介绍