One 、 Database login and data definition

1、 Log in to the database

Start by opening Mysql In the installation directory bin Catalog , Then enter... In the address field cmd, enter . My is installed in C disc .
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Enter the command line interface , And enter the mysql -u root -p, Enter and enter the password , The following screen is displayed , Indicates successful login .

 Input 'help' or '\h', view help . Input  '\c'  Clear the current input statement 

Input help after , There is one Note： All statements should be followed by ; end . This point and Navicat The rules in are different . Attention .

So let's get started ~

2、 Query which databases are

show databases;

3、 Create database

create database Database name ;

create database test;

At this time, the database is found test Created successfully . After entering test database

use test

then , There are no tables in our database , So let's create a student table first stu, Containing fields sno ,snames,sage,ssex

4、 Create table

create table stu (
sno char(10) primary key,
sname varchar(25) not null,
sage int,
ssex varchar(2));

Then use show tables; Command query database test All the tables in .

5、 see stu Table structure of table

desc stu;

6、 Modify table structure

① Give the data sheet stu Add fields sdept

alter table stu add sdept varchar(20);

② Delete sdept Field

alter table stu drop sdept;

③ Delete test database

drop database test;

Two 、 Add, delete, change and check the database

Because of our data sheet stu No data yet , So let's talk about how to insert data first

1、 Insert data into

When inserting data , You can have one insert Statement inserts a row , You can have one insert Statement insert multiple lines , Let's demonstrate separately

-- One insert Insert a row 
insert into stu values('2021001',' Cao Cao ',23,' male ');

-- One insert Insert multiple rows 
insert into stu values('2021002',' Xu Chu ',22,' male '),
				('2021003',' Lyu3 bu4 ',25,' male '),
				('2021004',' The sable cicada ',24,' Woman ');

After successfully inserting data , We begin to inquire

2、 Data query

Inquire about stu All records in the table

select * from stu;

3、 Data update

Change the age of Cao Cao to 25 year

update stu set sage=25 where sname=' Cao Cao ';

4、 Data deletion

Delete age less than 23 The record of

delete from stu where sage<23;

Not praising is equal to whoring in vain , Not praising is equal to whoring in vain , Not praising is equal to whoring in vain ~