string dbPath = @"D:\历年高考分数.db";
            string sq = @"Data Source=" + dbPath;
            m = new SQLiteConnection(sq);
            m.Open();
            SQLiteDataAdapter mAdapter = new SQLiteDataAdapter("select yxlc,gzl from 曲线三 where gzl=('a'+'b'+'c')",m);
            //SQLiteDataAdapter mAdapter = new SQLiteDataAdapter("select yxlc,gzl from 曲线三 where gzl=(a+b+c)", m);
            //SQLiteDataAdapter mAdapter = new SQLiteDataAdapter("select yxlc,gzl from 曲线三 where gzl=abc", m);
            //SQLiteDataAdapter mAdapter = new SQLiteDataAdapter("select yxlc,gzl from 曲线三 where gzl=a-b-c", m);
            DataSet ds = new DataSet();
            mAdapter.Fill(ds);
            DataTable dt = ds.Tables[0];
            //设置图表的数据源
            chart1.DataSource = dt;
            chart1.Series[0].IsVisibleInLegend = false;//是否显示图例
            chart1.Series["Series1"].ChartType = SeriesChartType.Spline;//形状
            chart1.Series[0].XValueMember = "yxlc";//X轴数据成员列
            chart1.Series[0].YValueMembers = "gzl";//Y轴数据成员列
                        chart1.DataBind();
            chart1.BringToFront();
            m.Close();

令a=combox1.text，b=combox2.text,c=combox1.text，
X值取yxlc列。a=CHR1，b=拖车1位，c=1002时，y取CHR111002列；a=CHR1，b=拖车1位，c=1009时，y取CHR111009列；a=CHR1，b=拖车2位，c=1009时，y取CHR121009列；等等（一共125列）
即如何使三个下拉框选好后，gzl列根据选的值取代对应的列