Let's learn about MySQL database

1. What is a database?

A database is a type of software that manages data. Data management is reflected in two aspects: the first is to describe data, that is, how to represent a piece of data; the second is to organize data, that is, how to manage a lot of data.

The main purpose of the database is to add, delete, modify and query data.

2. Classification of databases?

數據庫主要分為關系型數據庫和分關系型數據庫。

3. The difference between database and data structure

Data structure: It is an abstract subject that studies the logical structure and physical structure of data and their interrelationships, defines operations that are appropriate for this structure, and designs corresponding algorithms.

Database: It is a more specific type of software, and many data structures are used in the process of implementing this software.

Many software require data structures to implement additions, deletions, modifications and queries, and databases are just one of the application scenarios.

4. Introduction to MySQL database

4.1 Composition of MySQL Database

MySQL database is a "client-server" program. The client is the party that actively initiates the request. The data sent by the client is called a request. The server is the party that passively accepts the request. The data returned by the server is called a response. The client and server communicate through the network.

When installing the MySQL database, you can install the client and server on the same host or on different hosts. In actual situations, the same server can provide services to multiple clients.

Mainstream MySQL versions: MySQL 5 series, MySQL 8 series.

4.2 Introduction to MySQL Server

The MySQL server contains several databases, each of which is a logical collection of data tables (putting related tables together).

Server: contains multiple databases

Database: contains multiple tables

Table: contains multiple rows, each row is a record

Row: contains multiple columns, each column is a field

4.3 Data storage location of MySQL database

Many databases store data in external memory, such as MySQL and Oracle, while a few databases store data in memory, such as Redis.

MySQL stores data on disk. Here are the reasons:

First, understand the difference between memory and hard disk:

The memory has less space, while the hard disk has more space; the memory is more expensive than the hard disk; if there is a power outage, the data in the memory will be lost, but the data on the hard disk will not be lost.

The requirements for storing data in the database are: large capacity because the amount of data is large; lower costs are expected; data is expected not to be lost after power failure and can be stored persistently; compared with memory, hard disks fully meet these requirements, so hard disks are chosen to store data.

If the amount of stored data is large, you can choose to use the following method:

①Add more hard disks

② Use multiple machines for storage and shard MySQL databases and tables.

Summarize

First, the classification of databases is introduced, which are divided into structured databases and unstructured databases. Secondly, the composition of MySQL database is introduced, that is, MySQL consists of client and server, and the server is the main body of MySQL. Finally, it is introduced that the MySQL server stores data on the hard disk because the hard disk has large capacity, is cheap and can achieve persistent storage.

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