试试这个

 DataTable dt =  new  DataTable（）; 
 dt.Columns.Add（  ColOne）; 
 dt.Columns.Add（  ColTwo）; 
 dt.Rows.Add（  aa， 10 跨度>）; 
 dt.Rows.Add（  cc， 20 跨度>）; 
 dt.Rows.Add（  bb， 30 跨度>）; 
 dt.Rows.Add（  dd， 40 跨度>）; 
 dt.NewRow（）; 

 dataGridView1.DataSource = dt; 
 dataGridView1.Rows [dataGridView1.Rows.Count-1] .Cells [  ColTwo ] .Value = dt.Rows.OfType< DataRow>（）。总和（k = >  Convert.ToDouble（k [  ColTwo]））; 

尝试使用以下查询，检查如果它工作

  SELECT  
 ColOne = ISNULL（ColOne，' 总计'），
 TotalSales = SUM（ColTwo）
 FROM  atable 
 GROUP   BY  ROLLUP（ColOne）

i want to add column total in the last rows and down of the column which i want to sum.
i have two column

ColOne ColTwo
abc 10
axd 20
xyz 30
pqr 40

how i add sum of column ColTwo in the last row.

What I have tried:

select sum(ColTwo) From Table1;

try with this

DataTable dt = new DataTable();
               dt.Columns.Add("ColOne");
               dt.Columns.Add("ColTwo");
               dt.Rows.Add("aa", 10);
               dt.Rows.Add("cc", 20);
               dt.Rows.Add("bb", 30);
               dt.Rows.Add("dd", 40);
               dt.NewRow();

               dataGridView1.DataSource = dt;
               dataGridView1.Rows[dataGridView1.Rows.Count-1 ].Cells["ColTwo"].Value = dt.Rows.OfType<DataRow>().Sum(k => Convert.ToDouble(k["ColTwo"]));

try with below Query, check if it works

SELECT
  ColOne = ISNULL(ColOne , 'Total'),
  TotalSales = SUM(ColTwo)
FROM atable
GROUP BY ROLLUP(ColOne)