--alter table HistoryData drop constraint PK_HistoryData
alter table HistoryData add constraint PK_HistoryData primary key (CollectionTime,Code)
更改主键
delete from HistoryData where CollectionTime between‘2014-09-01 00:00:00‘ and ‘2014-11-01 00:00:00‘and ID not in (
select id from (
select Code,CollectionTime,max(ID) id from HistoryData
where CollectionTime between‘2014-09-01 00:00:00‘ and ‘2014-11-01 00:00:00‘group by Code,CollectionTime) a)
删除重复的列。sql 语句删除主键、更改主键、删除重复列（多列组合）
原文：http://blog.csdn.net/syytem004/article/details/42169219
