MS Chart 折线图——去除时间中的时、分、秒，按天统计【转】

private void Form2_Load(object sender, EventArgs e)
{
            string sql1 = "select 关键词,时间,相同条数 from 条目表";
            OleDbCommand cmd1 = new OleDbCommand(sql1, conn);
            conn.Open();

            string sql0 = "delete from 统计表";    //将表中原有数据删除，即初始化总词频表
            OleDbCommand cmd0 = new OleDbCommand(sql0, conn);    //定义SqlCommand变量
            cmd0.ExecuteNonQuery();

            OleDbDataReader dr1 = cmd1.ExecuteReader();
            while (dr1.Read())
            {
                if (dr1["关键词"].ToString() != "" && !comboBox1.Items.Contains(dr1["关键词"].ToString()))
                    comboBox1.Items.Add(dr1["关键词"].ToString());
                string sql2 = "";
                if (dr1["时间"].ToString() != "")
                {
                    if (dr1["相同条数"].ToString() != "")
                        sql2 = "insert into 统计表(关键词,时间,相同条数) values('" + dr1["关键词"].ToString() + "' ,'" + Convert.ToDateTime(dr1["时间"].ToString()).ToShortDateString() + "'," + Convert.ToInt64(dr1["相同条数"]) + ")";
                    else
                        sql2 = "insert into 统计表(关键词,时间,相同条数) values('" + dr1["关键词"].ToString() + "' ,'" + Convert.ToDateTime(dr1["时间"].ToString()).ToShortDateString() + "',0)";
                    OleDbCommand cmd2 = new OleDbCommand(sql2, conn);
                    cmd2.ExecuteNonQuery();
                }
            }
            dr1.Close();
            conn.Close();
            this.comboBox1.SelectedIndex = 0;

}

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            chart1.Series["不带转载发文量"].Points.Clear();
            chart1.Series["带转载发文量"].Points.Clear();

            string d_before = DateTime.Now.ToShortDateString();
            string w_before = DateTime.Now.AddDays(-30).ToShortDateString();
            string sql = "select 时间,count(*) as 条数 from 统计表 where 关键词='" + comboBox1.SelectedItem.ToString() + "' and 时间 between #" + w_before + "# and #" + d_before + "# group by 时间 order by 时间";
            OleDbCommand cmd = new OleDbCommand(sql, conn);
            conn.Open();
            OleDbDataReader rd = cmd.ExecuteReader();
            time.Clear();
            while (rd.Read())
            {
                if (rd["时间"].ToString() != "")
                {
                    chart1.Series["不带转载发文量"].Points.AddXY(Convert.ToDateTime(rd["时间"]).ToShortDateString(), rd["条数"]);
                   time.Add(Convert.ToDateTime(rd["时间"]).ToShortDateString());
                }
            }
            rd.Close();
            conn.Close();

            for (int i = 0; i < time.Count; i++)
            {
                string sql2 = "select 相同条数 from 统计表 where 关键词='" + comboBox1.SelectedItem.ToString() + "' and 时间 like '%" + time[i] + "%'";
                OleDbCommand cmd2 = new OleDbCommand(sql2, conn);
                conn.Open();
                OleDbDataReader dr = cmd2.ExecuteReader();
                int total = 0;
                while (dr.Read())
                {
                    int s2 = 0;
                    if (dr["相同条数"].ToString() == "")
                    {
                        s2 = 0;
                    }
                    else
                        s2 = Convert.ToInt32(dr["相同条数"]);
                    total += s2 + 1;
                }
                dr.Close();
                conn.Close();
                chart1.Series["带转载发文量"].Points.AddXY((time[i]), total);
            }
        }