Differences between SQL and NoSQL of mongodb series

When selecting a data store , Relational databases are often chosen (SQL) And non relational databases (NoSQL) Data storage , These two kinds of data have their own advantages and disadvantages , Here is a simple comparison

Relational databases vs. non relational databases

The main difference ：

1. Definition
   SQL Databases are called relational databases (RDBMS); and NoSQL Databases are called non relational databases or distributed databases

2. Distributed
   SQL To support distribution, you need to rely on some third-party components , such as mycat Etc , and NoSQL The database supports distributed by default , In band distributed solutions

3. structure
   SQL It stores data based on tables , therefore SQL Is a structured query language , Modifying the table structure may affect the system data storage . and NoSQL The database is a key value pair 、 Document based 、 Graphic database or wide column storage, etc , therefore NoSQL The database has a dynamic schema for unstructured data .

4. Inquire about
   SQL You can perform multi table joint queries , therefore SQL Can handle complex business , Perform complex multi table Association queries ;NoSQL The storage structure is not fixed , It can be key/value Key value of , It can also be document oriented 、 Column oriented 、 Graphics based . therefore SQL It is more suitable for applications that need multi line transactions

5. Business
   SQL Follow strict transaction consistency , That is to say ACID attribute ( Atomicity 、 Uniformity 、 Isolation and persistence ), and NoSQL The database follows A distributed CAP Theorem （ Uniformity 、 Availability and partition fault tolerance ）.

6. expand
   Sometimes SQL Database performance , You can add CPU or SSD And so on to increase the load of a single server . and NoSQL It can be done by slicing or in NoSQL Add more servers to the database

Relational database	NoSQL database
Relational database management system RDBMS	Non relational distributed database system
Distributed... Is not supported	Distributed is supported by default , Built in distributed solutions
Structured query language	NoSQL The database has a dynamic schema for unstructured data
Suitable for complex association query	It is not suitable for complex association query
follow ACID attribute	follow CAP() follow CAP（ Uniformity 、 Usability 、 Partition tolerance ）
You can add CPU or SSD And so on to increase the load of a single server	It can be divided into pieces or in NoSQL Add more servers to the database
Example ： MySQL、PostgreSQL、Oracle、SQL Server etc.	Example ： MongoDB、GraphQL、HBase、Neo4j、Cassandra etc.

Legend from ：https://www.pdai.tech/md/db/nosql-mongo/mongo-x-basic.html