兴起原因
关系数据库无法满足Web2.0的需求：1.海量数据的管理需求；2.数据高并发的需求；3.高扩展性和高可用性的需求。关系数据库的关键特性在Web2.0时代成为“鸡肋”：1.Web2.0网站系统通常不要求严格的数据库事务；2.Web2.0并不要求严格的读写实时性；3.Web2.0通常不包含大量复杂的SQL查询。
The reason for the rise
Relational databases cannot meet the needs of Web2.0: 1. The management needs of massive data; 2. The needs of high data concurrency; 3. The needs of high scalability and high availability. The key features of relational databases have become "chicken ribs" in the Web2.0 era: 1.Web2.0 website systems usually do not require strict database transactions; 2.Web2.0 does not require strict real-time read and write; 3.Web2.0 Usually does not contain a lot of complex SQL queries.
NoSQL数据库的特点：
1.灵活的可扩展性
2.灵活的数据模型
3.与云计算紧密融合
Features of NoSQL databases:
1. Flexible scalability
2. Flexible data model
3. Close integration with cloud computing
NoSQL的四大类型
1.键值数据库
会使用一个哈希表，这个表中有一个特定的Key和一个指针指向特定的Value。Value可以用来存储任意类型的数据，包括整型、字符型、数组、对象等。
1. Key-value database
A hash table is used, which has a specific Key and a pointer to a specific Value. Value can be used to store any type of data, including integers, characters, arrays, objects, etc.
2.列族数据库
数据库由多个行构成，每行数据包含多个列族，不同的行可以具有不同数量的列族，属于同一列族的数据会被存放在一起。
2. Column family database
The database consists of multiple rows, each row of data contains multiple column families, different rows can have different numbers of column families, and the data belonging to the same column family will be stored together.
3.文档数据库
文档数据库既可以根据键（Key）来构建索引，也可以基于文档内容来构建索引。
3. Document database
Document databases can build indexes based on keys or based on document content.
4.图数据库
以图论为基础，一个图是一个数学概念，用来表示一个对象集合。
4. Graph Database
Based on graph theory, a graph is a mathematical concept used to represent a collection of objects.
参考资料：百度百科
翻译：Google翻译
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