sql 语句删除主键、更改主键、删除重复列（多列组合）

--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。