sql基础知识点

1.用到SQL(structured query language )处理的数据库：mysql,access,SQL server,oracle,DB2,Sybase等.

2.RDBMS(relational database management system):关系型数据库管理系统

#（使用SQLyog）创建一个数据库语句

CREATE DATABASE practive

#创建一个表

CREATE TABLE Websites( 
id INT(5) NOT NULL AUTO_INCREMENT, 
NAME VARCHAR(10) NOT NULL, 
url VARCHAR(50) NOT NULL, 
alexa INT(10) NOT NULL, 
country VARCHAR(10) NOT NULL, 
PRIMARY KEY (`id`) 
) ENGINE=INNODB CHARSET=utf8; 

#插入数据

INSERT INTO websites (NAME,url,alexa,country) VALUES
('Google','https://www.google.cm/',1,'USA');

INSERT INTO websites(NAME,url,alexa,country) VALUES
('淘宝','https://www.taobao.com/',13,'CN')

INSERT INTO websites(NAME,url,alexa,country) VALUES
('菜鸟教程','http://www.runoob.com/ ',4689,'CN')

INSERT INTO websites(NAME,url,alexa,country) VALUES
('微博','http://weibo.com/',20,'CN');

INSERT INTO websites(NAME,url,alexa,country) VALUES
('Facebook',' https://www.facebook.com/ ',3,'USA')

#表图：

#查询语句

SELECT NAME,url FROM practive.`Websites`;

#查询一个列段的不重复显示

SELECT DISTINCT country FROM websites;

#要以两个列进行排序中间用逗号，而不是and符号

SELECT*FROM websites GROUP BY country,alexa

#更新表数据

UPDATE websites SET alexa = 5000,country='USA' WHERE NAME = '菜鸟教程'

#删除表特殊字段

DELETE FROM websites WHERE NAME='Facebook' AND country = 'USA';

#整理基础语言

SELECT*FROM websites 
WHERE country = 'CN' 
GROUP BY alexa DESC