Is there a way to add a column after a filled DataTable from SQL with the same rows?

Question

My problem is that not to add rows like filled by SQLDataAdapter at the same row in DataGridView. How to make that? I showed below the details with my code also a screen shot, which shows the rows differences from the origin one.
I don't want to add an expression as column behave in my sql script to get what I need with query result. I don't want to obtain that way.
using (SqlConnection c = new SqlConnection(ConnStrMSSQL))
c.Open();
// 2
// Create new DataAdapter
using (SqlDataAdapter a = new SqlDataAdapter("SELECT SIPNO, SERINO, TARIH FROM SNOHAREKETLER WHERE Cast(TARIH as DATE) BETWEEN '2015/03/20' AND '2015/03/20' AND (TEZNO = 'T23' OR TEZNO = 'T31') AND CIKTI is null", c))
// 3
// Use DataAdapter to fill DataTable
DataTable t = new DataTable();
a.Fill(t);
t.Columns.Add("MyColumn", typeof(string));
DataRow workRow;
int iGetCount = t.Rows.Count;
for (int i = 0; i <= iGetCount - 1; i++)
workRow = t.NewRow();
workRow["MyColumn"] = i;
t.Rows.Add(workRow);
dataGridView1.DataSource = t;

Answer 1

The extra column isn't applied to only certain rows.  The columns of a table identify what data each row will contain.  Hence adding a column to the table automatically adds them to the rows.  What you're seeing is that all the initial rows
aren't being assigned a value so they retain their default value of null.  Later you enumerate the rows of the existing table and call AddRow which adds new rows.  This isn't adding columns, but rows.
To generate values for the existing rows you should ideally simply pass the data back from the database.  DT computed columns can be difficult to set up as it is limited to what it can do.  If you want to use a computed column on the Datatable
itself then define the column as a computed column and every row will calculate its own value.
DataTable data = GetData();
//Add elapsed time column
var col = new DataColumn("ElapsedTime", typeof(TimeSpan), "expr");
data.Columns.Add(col);
dataGridView1.DataSource = data;
The issue you will run into however is that calculating a diff on DateTime doesn't work in a computed column as the expression doesn't support the necessary functions.  You can google for how people solved this if you are interested in alternatives. 
Most people just tend to add the column and then hook into the various change events to update the value as needed.