以前还真没这么干过，都是手工去掉约束，再添加的，今天一边google一边搞啊搞啊的，最终下面这个脚本可以用了
alter table dbo.SOTransaction
alter column UnitCostWithoutTax decimal(10, 2) not null
go
declare @name varchar(1000)
declare @tablename varchar(1000)
declare @fieldname varchar(1000)
set @tablename = ‘SOTransaction’;
set @fieldname = ‘UnitCostWithoutTax’;
select @name = b.name from syscolumns a inner join sysobjects b
on b.id=a.cdefault
where
a.id= object_id(@tablename)
and a.name=@fieldname
and b.name like ‘DF%’
–print @name
exec(’ alter table SOTransaction drop constraint ‘ + @name);
go
alter table dbo.SOTransaction
add constraint DF_SOTransaction_UnitCostWithoutTax default (0) for UnitCostWithoutTax