測試透過，那是相當的順利

--exec add_column "net_code","dddr",""

create proc add_column

@table varchar(100),--表名

@columns varchar(100),--欄位名

@type varchar(100)--資料型別（如不設定，預設為varchar(100)）

as

declare @sql varchar(3000),@type_code varchar(100)

if @type=""

begin

set @type_code="varchar(100)"

end

set @sql="if NOT EXISTS (select a.Name as columnName

from syscolumns as a

, sysobjects as b where a.ID=b.ID

and b.Name="""+@table+"""

and a.name="""+@columns+""")

BEGIN

alter table "+@table+" add "+@columns+" "+@type_code+"

select a.Name as columnName

from syscolumns as a

, sysobjects as b where a.ID=b.ID

and b.Name="""+@table+"""

END

ELSE

BEGIN

PRINT ""欄位已經存在！""

END

"

--print @sql

exec(@sql)