declare @typeid int
declare @tablename varchar(50)
declare @column varchar(50)

declare @sqlstr varchar(200)
declare @defaultid int

select @typeid = xusertype
 from systypes
  where name = @typename and xusertype > 256
  AND (is_member('db_owner') = 1 OR is_member('db_ddladmin') = 1 OR is_member(user_name(uid))=1)

declare mycursor cursor for
select o.name, c.name, c.cdefault
from syscolumns c, systypes t, sysusers u, sysobjects o
where c.xusertype = @typeid
 and t.xusertype = @typeid
 and o.uid = u.uid
 and c.id = o.id
  and o.type = 'u'

open mycursor
fetch next from mycursor into @tablename, @column, @defaultid
while @@fetch_status = 0
begin
  if @defaultid <> 0
  begin
    set @sqlstr = 'alter table ' + @tablename + ' drop ' + object_name(@defaultid)
    exec(@sqlstr)

    set @sqlstr = 'alter table ' + @tablename + ' alter column ' + @column + ' ' + @newtype
    exec(@sqlstr)
   
--    set @sqlstr = 'alter table ' + @tablename + ' add contraint ' + @tablename + 'df'+@column + ' default 0'

  end
  else
  begin
    set @sqlstr = 'alter table ' + @tablename + ' alter column ' + @column + ' ' + @newtype

    print @sqlstr
    exec(@sqlstr)
  end
  --if @@error <> 0
  --  continue
  fetch next from mycursor into @tablename, @column, @defaultid
end
--如果沒有約束，則可以直接刪除。如果有約束。先處理約束。

close mycursor
deallocate mycursor

end

GO

create procedure SP_CHANGEFIELD(@OLDTYPENAME VARCHAR(50), @NEWDTYPE VARCHAR(50))
as
begin

  exec('sp_addtype U_LOCALTYPE, ''' + @newdtype + '''')

  exec SP_rechangfieldtype @OLDTYPENAME, 'U_LOCALTYPE'

  EXEC sp_rebuildallview

  EXEC('sp_droptype ' + @OLDTYPENAME)

  EXEC('sp_addtype ' + @OLDTYPENAME + ', ''' + @newdtype + '''')

  exec SP_rechangfieldtype 'U_LOCALTYPE', @OLDTYPENAME

  EXEC sp_rebuildallview

  EXEC sp_droptype 'U_LOCALTYPE'

end
GO

--以下是示例。將U_HELLO的長度改為 30

SP_ADDTYPE U_HELLO, 'VARCHAR(10)'

GO
CREATE TABLE TESTTYPE(NAME U_HELLO)
GO

SP_CHANGEFIELD 'U_HELLO', 'VARCHAR(30)'