MySQL -- basic concept of database

Database system overview

What is data ？ What is a database ？ What is database management system ？ What is a database system ？

data (Data)

Symbolic records describing transactions become data . Phone number 、 full name

Data is the basic object stored in the database , In addition to the basic numbers 、 Like the name of a Book 、 Price 、 Authors and others can be called data .

for example ： In daily life , The information of a book can be described in this way ,《C Primer Plus》 It is a book published by the people's post and Telecommunications Publishing House , The author is prata (Prata S.), The price is 89.00, The date of publication is 2005 year 2 month 1 Japan , Such information can be described in the following way in the computer ：

• (C Primer Plus, People's post and Telecommunications Press , Prata (Prata S.),89.00,2005-2-1）

• namely , Put the information according to "（ The name of the book , Press. , author , Price , Publication date ）" Organized in a different way , This forms a record .

If there are multiple such records now , Then it can be listed in a table , Manage data through tables .

For example, there are several data types ：

• Book number 、 stock ： Integer data

• The name of the book 、 author 、 Press. ： String type

• Price ： Decimal type

Each row of data is called a record , Then the contents of each column are called fields . Each column has its own data type .

database (Database)

A warehouse for storing data .

Data should not only be stored , And it should be easy to read .

All the data is saved on the computer storage device , And the saved data will be stored in a certain format .

Database is stored in computer for a long time , organized 、 A collection of large amounts of data that can be shared . The data in the database is organized according to a certain data model 、 Description and storage , With less redundancy 、 High data independence and easy expansion , And can be shared by various users , So the database has permanent storage 、 There are three basic characteristics of organization and sharing .

In addition to the database , There should also be a database management system , To manage the data well .

Database management system (Database Management System,DBMS)

In addition to having a database , We also need to manage the database .

Organize and store data scientifically , It can efficiently acquire and maintain data .

The database management system is the same as the operating system , It is the basic software of computer , It is also a large and complex software system , The main functions include the following aspects ： Data manipulation function , Database transaction management and operation management 、 Data definition function , Data organization 、 The establishment and maintenance of storage and management data .

Database system (Database System,DBS)

Database system （Database System,DBS） It consists of hardware and software .

Hardware is mainly used to store data in the database , Including computers 、 Storage devices, etc . The software part mainly includes the database management system 、 An operating system that supports the operation of a database management system , And support the access technology of multi language application development .

Database system refers to the system after introducing database into computer system .

It is the foundation of the whole database , All databases need to access data through applications written by development tools , The data usually needs to be managed by the database administrator （Database Administrator,DBA） maintain .

What is? SQL

Structured query language

SQL Its pronunciation is letters S-Q-L or sequel, yes Structure Query Language（ Structured query language ） Abbreviation , Is currently widely used relational database standard language .

The language is written by IBM stay 20 century 70 Developed in the s , Be treated as IBM relational database System R Prototype relational language , Realize information retrieval in relational database .

The earliest support in the world SQL The standard is Oracle company , because SQL Easy to learn 、 Rich functions and flexible use , Therefore, it is sought after by many people . Through constant development 、 Perfection and expansion ,SQL By the National Bureau of standards （ANSI） American Standard for relational database language , Later, it was recognized by the international organization for standardization （ISO） International standards adopted as relational database language . Almost all relational database management system software supports SQL, Many manufacturers are also right SQL The basic commands have been expanded to varying degrees .

NoSQL Don't use SQL → no only SQL

SQL Language has the following parts ：

• Data operation language （Data Manipulation Language,DML）

  Realize the operation of data , Used to retrieve or modify data .

• Data definition language （Data Definition Language,DDL）

  Structure used to define data , establish 、 Modify or delete database objects .

• Data control language （Data Control Language,DCL）

  Used to control the permissions of database users .

• Transaction control （Transaction Control,TCL）

  It defines the relevant commands including the start and end of the transaction .

• DDL Included sub parts

  • Integrity constraints （integrity constraint) Whether the inserted data meets the requirements , If you don't meet the needs, you won't be allowed to insert

  • View definition      (View Definition)      You can easily check some of our data

SQL Has the following advantages ∶

• SQL Not a specific database vendor's proprietary language . Almost all important database management systems support SQL, So just learn SQL Can interact with all databases .

• SQL Easy to learn , The sentences in this language are all made up of English words with strong description , And the number of these words is small .

• SQL Highly unprocessed , The box SQL Perform database operations , Just point out " What do you do ", No need to specify " How do you do it? ", The selection of access path and the execution of operation are automatically completed by the database management system .