--1、取得数据库所有表的默认值：

select

   t3.name   as   表名,t1.name   as   字段名,t2.text   as   默认值   ,t4.name

  from   syscolumns   t1,syscomments   t2,sysobjects   t3   ,sysobjects   t4

   where     t1.cdefault=t2.id   and   t3.xtype='u'   and   t3.id=t1.id

  and   t4.xtype='d'   and   t4.id=t2.id; 

---2、生成删除所有默认值的语句： 

select "ALTER  TABLE " +  t3.name   + " DROP  CONSTRAINT  " +t4.name  +";"

  from   syscolumns   t1,syscomments   t2,sysobjects   t3   ,sysobjects   t4

    where     t1.cdefault=t2.id   and   t3.xtype='u'   and   t3.id=t1.id

  and   t4.xtype='d'   and   t4.id=t2.id  ; 

---3、生成批量添加所有默认值的语句：

select "alter table " +  t3.name   + "  add default  (1)  for " +t1.name  +";"

from   syscolumns   t1,syscomments   t2,sysobjects   t3   ,sysobjects   t4

   where     t1.cdefault=t2.id   and   t3.xtype='u'   and   t3.id=t1.id

and   t4.xtype='d'   and   t4.id=t2.id ;