sql 表修改列

 create table #a
(
a int identity(1,1) primary key,
b int default(0) not null,
c nvarchar(20)
)
insert into #a(c)
select 'a' union all
select 'b' union all
select 'c' union all
select 'd' union all
select 'e'
select * from #a
alter table #a drop constraint DF__#a_____________b__1273C1CD
alter table #a add constraint DF__#a_____________b__1273C1CD  default(1) for b
alter table #a add  c nvarchar(10) not null constraint DF_#a_b default('aa')
--有约束的时候可以通过错误提示来查约束名
alter table 表名 drop column [列名]
alter table 表名 add [列名] [类型] NULL CONSTRAINT [DF_表名_列名] DEFAULT ((0))
select * from #a