查询多列数据时用这种方法查询

 private void cbbType_SelectedIndexChanged(object sender, EventArgs e)
        {
            //清空DN列
            cbbDn.Items.Clear();
            //字段清除
            FieldListSaddle.Clear();
            //加入字段
            FieldListSaddle.Add("Baojiao,Drawing,Table,Ribs,Type1,HasPad");
            //定义查询条件
            string where = string.Format("DnX < {0} and DnD >= {0} and Type2 = '{1}'", DI, cbbType.Text);
            //按照条件查询表
            tbBiao = GetAccessData(TypeName, FieldListSaddle, where);
            //如果表中有两列数据则需要循环查找并添加
            for (int i = 0; i < tbBiao.Rows.Count; i++)
            {
                //表名等于第一行数据的表
                string TableName = (tbBiao.Rows[i]["Table"]).ToString();
                //查询出DN表放入内存
                tbDn = GetAccessData(TableName);
                //查询出符合DN的那一列
                DnList = tbDn.AsEnumerable().Select(p => p.Field<double>("DN").ToString()).Distinct().ToList();
                //加入控件中
                cbbDn.Items.AddRange(DnList.ToArray());
            }
        }