Change Data Table From System.data Into Sql Query

i someone had teach me how to write a query in datatable. however i need to get the data out from my database rather than the data table. can someone teach me how should i do it?
esp at the first like.... like DataTable dt = GetFilledTable()
 since i already have set of data in my preset table i should be getting data from SqlDataSource1 right ( however i am writing this in my background code or within <script></script>
 so can anyone help me?


 
 
 
protected void lnkRadius_Click(object sender, EventArgs e)
    
    {
    
        DataTable dt = GetFilledTable();
    
    
    
        double radius = Convert.ToDouble(txtRadius.Text);
    
        decimal checkX = (decimal)dt.Rows[0]["Latitude"];
    
        decimal checkY = (decimal)dt.Rows[0]["Longitude"];
    
    
    
        // expect dt[0] to pass - as this is our check point
    
        // We use for rather than fopreach because the later does not allow DELETE during loop execution
    
        for(int index=0; index < dt.Rows.Count; index++)
    
        {
    
            DataRow dr = dt.Rows[index];
    
    
    
            decimal testX = (decimal)dr["Latitude"];
    
            decimal testY = (decimal)dr["Longitude"];
    
    
    
            double testXzeroed = Convert.ToDouble(testX -= checkX);
    
            double testYzeroed = Convert.ToDouble(testY -= checkY);
    
    
    
            double distance = Math.Sqrt((testXzeroed * testXzeroed) + (testYzeroed * testYzeroed));
    
    
    
            // mark for delete (not allowed in a foreach - so we use "for")
    
            if (distance > radius)
    
                dr.Delete();
    
        }
    
    
    
        // accept deletes
    
        dt.AcceptChanges();
    
    
    
        GridView1.DataSource = dt.DefaultView;
    
        GridView1.DataBind();
    
    }