（1）select語句

select * from website

select name from website

select name country? from website

（2）在表中一個列可能包含多個重復(fù)值，有時候希望列出不同（distinct）的值

select distinct country from websites

（3）where子句用于提取那些滿足制定標準的記錄

select * from Websites where country = ‘CN’;

select * from websites where id= 1;

SQL使用單引號來引用文本值，文本字段使用單引號，數(shù)字字段不使用

（4）如果在第一個條件第二個條件都成立，則and運算符顯示一條記錄，只有一個成立則是OR

select * from Websites where country = ‘CN’ and alexa >50;

select * from Websites where country = ‘USA’ or country = ‘CN’;

select * from Websites where alexa >15 and (country = ‘CN’ or country = ‘USA’);

(5)order by 關(guān)鍵字用于對結(jié)果集按照一個列或者多個列進行排序，默認升序，降序desc

select * from Websites order by alexa;

select* from Websites order by alexa DESC;

select *from Websites order by country, alexa;

(6)insert into用于向表中插入新記錄

假如像websites表中插入一個新行

insert into websites (name, url, alexa,country) values(‘百度’，’https://www.baidu.com/’,’4’,’CN’);

在指定列插入數(shù)據(jù)

insert into Websites (name,url, country)values (‘stackoverflow’,’http://stackoverflow.com/’,’IND’);

(7)update用于更新表中存在記錄

update Websites set alexa = ‘5000’,country = ‘USA’ where name=‘菜鳥教程’;

(8)用于刪除表中的行

delect from Websites where name= ‘百度’ and country=‘CN’;

不刪除表情況下刪除所有行

delect from Websites或 delect * from Websites