这两课主要介绍sql中利用select语句对数据的简单检索。
下面分别讨论不同类型的检索

检索列

单个列

select prod_id
from Products;

多个列

select prod_id, prod_name, prod_price
from Products;

所有列

select *
from Products;

检索不同值 的列

select distinct vend_id
from products;

检索前几列或者后几列

select prod_name
from products
limit 5;

select prod_name
from products
limit 5 offset 5;

检索排序数据

单个列排序

select prod_name
from products
order by prod_name;

多个列排序

select prod_id, prod_price,prod_name
from products
order by prod_price,prod_name;

指定排序的方向

select prod_id, prod_price,prod_name
from products
order by prod_price desc, prod_name;