问题：对于表 TestData : ID, DataID, A,B,C，需要删除DataID重复的记录，仅保留第一条。 ID为Int型主键。

delete *  from  TestData
where ID not in
(
select Min(ID) from TestData
group by DataID
)

解答：大容量记录删除时，我这样写：

delete *
from TestData
Inner Join
(select [Type]), Min(ID) as MinID from TestData group by [Type]) T
On TestData.[Type])=T.[Type])
Where TestData.ID>T.MinID