Question

sql server 怎么查询一个列中有多少种不同的值

例 表 Question
QID QName Difficulty
1 "张三" 2
2 "李四" 1
3 "王五" 2

想查询Difficulty字段有多少种不同的值，各是什么？

Answer 1

select distinct Difficulty from Question
或者
select Difficulty from Question
group by Difficulty

Answer 2

select distinct count(difficulty) from question
select distinct difficulty from question