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MySQL - Database Foundation

2022-06-21 10:48:00 【Longbow dog learning C】

Catalog

One . What is a database

File saving data has the following disadvantages

File security issues
Files are not conducive to data query and management
Files are not conducive to storing large amounts of data
It's not convenient to control the file in the program

So in order to solve the above problems , More effective data management , Database came into being .

Two . Mainstream databases

SQL Sever： Microsoft products ,.Net Programmer's favorite , Medium and large scale projects .
Oracle： Oracle products , Suitable for large projects , Complex business logic , Concurrency is generally not as good as MySQL.
MySQL： The world's most popular database , It belongs to Oracle , Good concurrency , Not suitable for complex business . Mainly used in e-commerce ,SNS, Forum . For the simple SQL The treatment effect is good .
PostgreSQL : A relational database developed by the computer department of the University of California, Berkeley , Whether it's for private use , commercial , Or for academic research , Free to use , Modify and distribute .
SQLite： It's a lightweight database , Abide by ACID Database management system based on RDBMS , It's contained in a relatively small C In the library . Its design goal is embedded , And it has been used in many embedded products , It takes up very low resources , In embedded devices , It may take only a few hundred K That's enough memory .
H2： It's a use. Java Development of embedded database , It itself is just a class library , It can be directly embedded into the application project .

3、 ... and . Basic use

You need to install on your own server first , The blogger bought the ECS here +Xshell The use of . Please operate in the station as shown in the figure , You can find a number of installation tutorials , I won't go into details here .

Connect to server

mysql -h 127.0.0.1 -P 3306 -u root -p
mysql -uroot -p At present, only the second type can be connected , The problem remains to be solved .

If not -h 127.0.0.1 The default is to connect locally
If not -P 3306 Connection by default 3306 Port number

The server , database , Table relations

Install the server , Is to install a database management program system program on the machine , You can manage multiple databases , Generally, an application pair uses a database . The corresponding relationship is as follows ：

Code operation

// Create database 
creat database base1;

// Using a database 
use base1;

// Create database tables 
creat table person(
    id int,
    name varchar(32),
    gender varchar(2)
);

// Insert data into the table 
insert into person(id,name,gender)values(1,' One person ',' male ');
insert into person(id,name,gender)values(2,' Person two ',' male ');
insert into person(id,name,gender)values(3,' Three people ',' Woman ');

// Query data in table 
select * from person;

SQL classification

DDL【data definition language】 Data definition language , Used to maintain the structure of stored data
For instructions : create, drop, alter
DML【data manipulation language】 Data manipulation language , Used to manipulate data
For instructions ： insert,delete,update
DML There is another one in the DQL, Data query language , For instructions ： select
DCL【Data Control Language】 Data control language , Mainly responsible for authority management and affairs
For instructions ： grant,revoke,commit