MySQL: understand the basic knowledge of MySQL and computer

《MySQL》 Get to know MySQL Basic knowledge of computer

Preface :

This chapter mainly explains the basic knowledge of database and MySQL Knowledge about .

1 Study MySQL

MySQL The main learning contents of :

• Basic operation of database , With SQL Statement is the core (SQL Is a programming language )

• The underlying principle of database ( Is difficult )

• Database programming ( adopt java Code operation database )

2 What is a database

2.1 Database introduction

As the name suggests, database is actually a tool for managing data . It's a software

Databases are divided into relational databases and non relational databases

There are also many relational database software :

• MySQL

  Open source , At present, databases with a large share in the market , It is also a database for classroom learning

• Oracle

  charge , ( It costs a lot ), Generally, it is used to have high requirements for data security Oracle It costs a lot of money , Chinese companies have opened " Go to Oracle" motion , Continuous improvement MySQL, send MySQL Has been greatly developed . Become one of the most powerful databases in the world . These two databases belong to Oracle company .

• SQL server

  Microsoft's database , Generally, many schools use SOL server To explain the database .

• SQLite

  This database is the largest installed database in the world , It is the built-in database of Android .

Non relational database :

• Redis

• MongoDB

• HBase

• …

2.2 install MySQL database

install MySQL: mysql Install video _ Bili, Bili _bilibili

It is recommended to set the password to simple , Avoid forgetting …

MySQL Client interface :

3 MySQL structure

3.1 MySQL It's a " client – The server " structure

• client : The party who made the request voluntarily -> Data sent by the client to the server , be called " request "

• The server : The party that responded passively -> The data returned by the server to the client , be called " Respond to "

A server can provide services for multiple clients at the same time .

The general server is 24 Running in hours , Serve clients anytime, anywhere .

installed MySQL, We installed the client , The server is also installed .

MySQL in , Storing and managing data , It's all by MySQL The server is responsible for , Because of that ,MySQL The server of is much more complex than the client , So generally, when interviewing , talk about MySQL Generally, it directly replaces the server !!!

3.2 MySQL Organization data

One MySQL The server can manage multiple " database "( The database here is not software , It is the place where related data is stored , That is, the collection of data )

Data can be stored together , But in order to avoid mutual interference between data , Therefore, the data is logically separated .( That is to store data in different databases )

There are multiple data tables in each data .

Each table has multiple rows , Each line is called a record

Each row has multiple columns , Each column has different meanings , Also known as a " Field "

Whether it's Oricle still MySQL, As long as it's a relational database , Data is stored in the above way .

4. The von Neumann system

Von Neumann :

The von Neumann system :

• CPU

• Memory -> A device that stores data

• input device

• Output devices

Computers store data in binary .

Memory is divided into external memory and memory :

• Memory : That is, what we usually call memory , For temporary storage CPU Operation data in , And data exchanged with external memory such as hard disk .

• External storage : External memory refers to memory other than memory , This kind of storage can still be stored after power failure .

  for example : Hard disk , Compact disc , floppy disk

The difference between memory and external memory ( a key )

1. Memory storage space is relatively small , The storage space of external memory is relatively large

2. CPU Reading data from memory is faster , and CPU Reading data from external memory is slow ( Difference between 3-4 An order of magnitude )

3. The price of memory is much higher than that of external memory

4. The data on the memory will be lost when it is powered off , The data stored outside will not be lost after power failure .

MySQL Store data on hard disk

So in the actual development , Generally, performance bottlenecks tend to appear in the database .

5. MySQL Simple operation of

Rule of grammar :

SQL Keyword is case insensitive

Semicolons cannot be forgotten , Some statements can be without semicolons , But if you add it, you won't report an error .

Error information when keyword input is wrong :

5.1 Create database

create database  Database name ;

5.2 Display database

show databases;

5.3 Select database

When we need to perform specific operations on data , You need to select the database to operate

use  Database name ;

summary :

This chapter focuses on understanding MySQL As well as MySQL Relevant computer foundation …