SQL基础

Posted 2020-08-29 Churjan

一、mysql管理指令

/Applications/XAMPP/xamppfiles/bin/mysql -uroot

1.显示所有的库

SHOW DATABASES;

2.进入mysql库

USE mysql;

3.显示当前显示的库

SELECT DATABASE();

4.显示当前库中所有表名称

SHOW TABLES;

5.查询sql表名的所有记录

SELECT * FROM sql;

6.退出mysql服务器

exit;

#查询当前MySQL编码

#已导入sql文件的方式  source d:/xx.sql

 

二、

SQL语句的分类
1:DDL Data Define Language
定义库的特征，表的结构--操作列

CREATE/DROP/ALTER/TRUNCATE

CREATE DATABASE crm;

CREATE DATABASE crm1 CHARACTER SET UTF8;

CREATE TABLE student(

　　id INT PRIMARY KEY AUTO_INCREMENT,

　　name VARCHAR(25),

　　score DOUBLE(10,2),

　　birthday DATE

);

DROP DATABASE crm1;

DROP DATABASE student;

ALTER TABLE student ADD sex VARCHAR;

ALTER TABLE student DROP birthday;

ALTER TABLE student MODIFY score INT;

 

2:DML Data Manipulate Language
操作表中的记录行--操作行
INSERT/DELETE/UPDATE

 

INSERT INTO student VALUES(null,‘Churjan‘,99,‘1993-8-14‘);

INSERT INTO student(部分列名) VALUES(...);

DELETE FROM student WHERE score=99;

UPDATE student SET score=score/2 WHERE name=‘Churjan‘;

3:DQL Data Query Language***
SELECT

 

 

SELECT * FROM student ORDER BY score;  //升序

SELECT * FROM student ORDER BY score DESC;  //降序

4:DCL Data Control Language
控制数据库用户的权限
GRANT/REVOKE

三、sql函数

MAX();

MIN();

AVG();

COUNT();

SUM();