What is a database?

You can use files to store data, why do you need a database?

Files save data have the following disadvantages:
File security issues
Files are not conducive to data query and management
Files are not conducive to storing massive data
Files are inconvenient to control in the program
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Database storage medium:
Disk
Memory

In order to solve the above problems, experts have designed something more conducive to managing data - database, which can manage data more effectively.The level of the database is an important indicator to measure the level of a programmer.

Software angle

Document Angle

Database composition:

Database server (musqld)
Database + table structure
Database client (mysql: is a client software)

The database is a web server

mysql or database belongs to the application layer
mysql OS:needs to be installed, the bottom layer must be the file interface that directly or indirectly accesses the OS

Basic usage

Server, Database, Table Relationships

The so-called database server installation is just a database management system program installed on the machine. This management program can manage multiple databases. Generally, developers will create a database for each application.
In order to save the data of the entities in the application, multiple tables are generally created in the database to save the data of the entities in the program.
The relationship between database server, database and table is as follows:

The so-called creation of a database is essentially to create a directory under Linux
The so-called creation of a database table is essentially to create a specific file in a specific directory!

Common basic operations

Common database operations

# show all your databasesshow databases;# Create a database (it is recommended not to use those databases that come with the system)create database (the name of the database you want to use);# Using the databaseuse (the database name you want to use);# Use the database you created first, and then display which tables are in your databaseshow tables;# show table structuredesc tables_name ;

Try it out

SQL Classification

DDL【data definition language】 Data definition language, used to maintain the structure of stored data
Represents instructions: create, drop, alter

DML【data manipulation language】Data manipulation language, used to operate on data
Representing instructions: insert, delete, update

DML is divided into a separate DQL, data query language,
represents the command: select

DCL【Data Control Language】 Data control language, mainly responsible for authority management and transactions
Representative instructions: grant, revoke, commit

Current system supported storage engines