过滤数据

select语句和where语句结合

select prod_name,prod_id from products where prod_price = 2.50;

这里返回prod_price=2.50的行的prod_name和prod_id列

select * from products where prod_price = 2.50;

这里返回prod_price=2.50的行的所有列

所有小于10美元的商品信息

select * from products where prod_price < 10;

这里注意，order by语句只能位于where语句之后，否则会出现语法错误，比如第二个语句

select * from products where prod_price <= 10 order by prod_price;

select * from products order by prod_price where prod_price <= 10;

where之<>不等于

select vend_id,prod_name from products where vend_id <> 1003;

select vend_id,prod_name from products where vend_id != 1003;类似

这是检索vend_id不是1003的商品信息

where语句对于字符类型的要使用单引号，对于数字型的则不需要，上下两个可以对比；

搜索检查范围  between  必须要有两个边界值，并且包含边界值

select vend_id,prod_name,prod_price from products where prod_price between 5 and 10 order by prod_price;

空值检查

select cust_id,cust_email from customers;

select cust_id from customers where cust_email is null;