1.别名查询，使用关键词as
select * from student as p;

列起别名：select name as ‘商品名’ ,price ‘价格’ from product;
去掉重复值：select distinct price from product;(去除price这一列重复的值)
select distinct * from student;(去除重复的行）

特殊使用：
select 6-2;
select 6/2;