.net在线更新SQL数据库

        SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnStr"].ConnectionString);
        //string sql = "Create   Table   testtable(test1   varchar   not   null   primary   key,test2   int)";
        string sql = "alter   table   test   add   test5 int default (0)";
        SqlCommand cmd = new SqlCommand(sql, con);
        cmd.Connection.Open();
        try
        {
            cmd.ExecuteNonQuery();
        }
        catch
        {
            //MessageBox.Show(ex.Message);
        }
        finally
        {
            cmd.Connection.Close();
        }