---添加主键
alter table test add [id] int identity(1,1)
--删除重复列
delete test where a not in (select top 1 [id] from test group by a,b,c,[id])
--消除主键
alter table test drop column [id]
---添加主键
alter table test add [id] int identity(1,1)
--删除重复列
delete test where a not in (select top 1 [id] from test group by a,b,c,[id])
--消除主键
alter table test drop column [id]