mysql 笔记二

//查询varchar刑

select * from user where name='gaogao';

//价格小于100元

select * from products where price<100;

//价格小于等于100元

select * from products where price<=100;

//查询姓名不是gaogao的

select * from user where name<>'gaogao'

//查询id 不是10的用户

select * from user where id<>10;

//用另一个 ！=

select * from user where id!=10;

//用between 限定范围

select * from user where id between10 and 20;

前一个是开始值，后一个是结束值

如果将20 和10替换掉，就得不到结果

//空值检查

null

select * from user where phone is null;

//逻辑操作符 and

select * from products where id<100 and price<50;

查询出前100个价格低于50元的商品

//or

select * from user where id=10 or id=11;

//or与 and  系统会默认调用and

select * from product where (id>100 or id<10) and price =50

//是查询id大于100或者小于10的商品中，价格为50的商品

如果不加（）

select * from product where id>100 or id<10 and price=50

解释为 id小于10并且价格为50的商品，获取id大于100的商品

//in在。。。里

select * from user where id in(10.20.30.40);

//not in 不在。。里,,找出与条件不匹配的行

select * from user where id not in (10.20.30);