Database, relational database and NoSQL non relational database

1. database （DataBase,DB）

database （DataBase,DB）： It refers to the storage device stored in the computer for a long time ( Hard disk ) On , Organize according to certain rules , A collection of data that can be shared by various users or applications , Or in the form of files on the server computer .

database （DataBase,DB）, Namely A warehouse for storing data , Data can be persisted , And pass sql Statement to quickly add, delete, modify and check the data CRUD operation （CRUDP： establish create, Read read, modify update, Delete delete, Pagination page）.

The main difference between database and ordinary file system （ cause ）： The database can quickly find the corresponding data .

database structure

• A database server software can create multiple databases （ An application corresponds to a database ）

• A database can create multiple tables                           （ A class corresponds to a table ）

• A table can store multiple records                               （ An object corresponds to a record ）

• The client connects to the database server software

SQL（Structure Query Language, Structured query language ）

SQL（Structure Query Language, Structured query language ））, adopt sql Operating the database ( Operating the database , Operation table , Operational data ).

SQL By the National Bureau of standards （ANSI） American Standard for relational database language , Later, it was organized by international standards organization （ISO） International standards adopted as relational database language . Database manufacturers (MySql,oracle,sql server) All support ISO Of SQL standard . Each database manufacturer has made its own extension on the basis of the standard . 

SQL The grammar of

• Each statement ends with a semicolon ( The command line needs ), If in navicat,Java It is not necessary to add in the code .

• SQL stay window Case insensitive in , In keywords, uppercase and lowercase are the same

SQL The classification of

DDL Data definition language	Data Definition Language	DDL Operating the database ,DDL Operation table
DML Data manipulation language	Data Manipulation Language	DML Operation table record - Additions and deletions
DQL Data query language	Data Query Language	DQL Operation table record - Inquire about
DCL Data control language	Data Control Language	The setting of user rights

2. Relational databases ： Stored on disk

A relational database is a database created according to a relational model . The so-called relationship model is “ one-on-one 、 One to many 、 Many to many ” And so on , A relational model is a two-dimensional tabular model , Therefore, a relational database is a data organization composed of two-dimensional tables and their relations .

Relational models include data structures （ The problem of data storage , Two-dimensional table ）、 Set of operation instructions （SQL sentence ）、 Integrity constraints ( Table data constraints 、 Constraints between tables ).

Common relational databases

MySQL	Free open source , Small and medium-sized database	Has been Oracle Acquisition （MySQL6.X The version also began to charge ）
OracleSQL	Rechargeable Large databases	Oracle Products of the company
DB2	Rechargeable In the banking system	IBM The company's database products
SQLServer	Rechargeable Medium sized database	MS company
SyBase	Has faded out of the stage of history	Provides a very professional data modeling tool PowerDesigner（ Founder Wang Xiaoyun ）
SQLite	Embedded small database	It's used on the mobile phone

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3. Non relational databases NoSQL（Not Only SQL）： Stored in memory

NoSQL（Not Only SQL, meaning “ not only SQL”）, It's a new database concept （ A general term for a non-relational database ）, It is a supplement to relational database , Not a substitute .

effect ： Dealing with data processing problems based on massive users and massive data .

NoSQL The advantages of ：

        1. Easy to expand

        2. Large amount of data , High performance

        3. Flexible data model

        4. High availability

In order to solve the three high problems , That's what we need NoSQL

Three high questions ：

        1.High performance - High concurrent read and write requirements for database

        2.Huge Storage - The need for efficient storage and access of massive data

        3.High Scalability && High Availability- The need for high scalability and high availability of databases

Solve the bottleneck of relational database , Non relational data is currently used as a supplement to relational databases .

common NoSQL Non relational database

classification	Related products	Application scenarios	advantage	shortcoming
The key stores the database (Key-Value)	Redis、MemCache	Content caching , Like conversation 、 The configuration file 、 Parameters, etc. ; Read and write frequently 、 Applications with simple data models	Good scalability , Flexibility , High performance in a large number of operations	Unstructured data , It is usually only treated as string or binary data , The value can only be queried through the key
Column family storage database ( Distributed )	HBase、Cassandra、 Bigtable	Distributed data storage and management	High scalability , Fast search speed , Low complexity	Functional limitations , Strong consistency of transactions is not supported
Document database <key,value> in value yes JSON Structured documents	MongoDB、CouchDB	Web application , Store document oriented or similar semi-structured data	Flexible data structure , According to value Build index	Lack of uniform query syntax
graphics (Graph) database	Neo4j、InfoGrid	Social networks 、 Recommendation system , Focus on building the relationship map	Support complex graphics algorithms	High complexity , It can only support a certain data scale