去重 DISTINCT、别名 AS

insert into studentdd
values
('张三',18),
('李四',18),
('王五',19),
('张三',18);--重复数据

--加distinct 去重
select distinct age from studentdd;

select
name AS 姓名,
age AS 年龄
from studentdd;

select
s.name,
s.age
from studentdd AS s;

select
DISTINCT age AS 不重复年龄
from studentdd;