1、uid、pwd --------user ID、password
2、select column1 ,column2 from tablename a
where column2=(select top 1 column2 from tablename where a.column2=column2)
2、select column1 ,column2 from tablename a
where column2=(select top 1 column2 from tablename where a.column2=column2)
insert into @b
select 1,'a' union
select 1,'b' union
select 2,'b' union
select 2,'c' union
select 2,'c' union
select 3,'d' union
select 3,'f'
select column1,column2
from @b a
where column2=(select top 1 column2 from @b where column1=a.column1)
--结果
-------------------
--column1 column2
--1 a
--2 b
--3 d