系统先distinct运算再top运算
SELECT DISTINCT TOP (10) orderid, id, mid, wid, bought FROM Merchandise WHERE (cityid = 0x3034323041323036) ORDER BY bought DESC
1.distinct：针对查询的结果去去除重复（主要针对查询的结果）
top获取前几条数据，top一般都与Order by连用（desc、asc）
distinct去除重复的数据
select distinct Sname from Student select top 5 * from Student order by tmath desc
2.查询前百分之30%，若不是整数比向上取整
select top 35 percent * from tableScore order by desc
3.distinct要放到top前面，这样取出的结果是先将数据Distinct去重复，然后再取其中的前两行
SELECT distinct top 2 LastName FROM [dbo].[Employees] order by LastName
4.去掉重复的数据，统计count数量:
select count(distinct(xtype)) from sysobjects
5.查询前100条，并且去掉重复数据:
select distinct top 100 xtype from sysobjects 同上 select count(distinct(sysstat)) from sysobjects select distinct top 10 sysstat from sysobjects select distinct top (select count(distinct(sysstat)) from sysobjects) sysstat from sysobjects
6.如果想要在去重后选出的数据中选出前三条，则应该将distinct写在top的前面：
SELECT DISTINCT TOP 3 USERNAME,PASSWORD FROM USERS WHERE SEX='男'
7.distinct会作用在多个字段上，没有办法按一个字段去重，再取出其它的字段：
#使用disctinct获取的内容 select * from t where x not in (select distinct x from t2) #取某字段非空的行 select * from miaopai.bt_micro_user where aweme_count is not null order by aweme_count desc limit 10 #count(disinct) select count(distinct publish_nick) from miaopai.bt_micro_user
8.去除重复数据，针对已查询出的整个结果集进行数据重复处理，而不是针对某一列。
select distinct sName from student select distinct sName,sAge from student
9.TOP关键字获取前几条数据，一般都与order by连用
select top 5 * from TblScore order by tMath asc --取数学成绩最低的前5个，升序排列 select top (2*2) from TblScore order by tMath desc --取数学成绩最高的前5个，降序排列，top后面如果是表达式，必须括起来
10. 取数学成绩最低的前%30，升序排列,百分比如果不是整数条，会向上取整（夺取一条）
select top 30 percent * from TblScore order by tMath asc
11.其他示例：
select * from Tbstudent where stuClassId in(1,3,4)
top关键字：查询前若干条记录
select top(5) * from Tbstudent where stuClassId in(1,3,4)
查询前百分之几条记录,按百分比查询出于顶端的记录，不按四舍五入，是直接进位
select top 20 percent * from Tbstudent select * from Tbstudent
distinct关键字：用来去除查询结构集中的重复记录
select distinct * from Tbstudent
查询所有的学生籍贯地
select distinct stuAddress from Tbstudent
