查询约束名
select b.name from syscolumns a,sysobjects b where a.id=object_id('表名') and b.id=a.cdefault and a.name='字段名' and b.name like 'DF%'
删除约束
alter table 表名 drop constraint 约束名
查询约束名
select b.name from syscolumns a,sysobjects b where a.id=object_id('表名') and b.id=a.cdefault and a.name='字段名' and b.name like 'DF%'
删除约束
alter table 表名 drop constraint 约束名