C# - EXPORT Dataset To EXCEL

I am using the following code to export fields from a database table into excel. What I want to do is be able to write a SQL statement to retrieve fields from multiple tables and export them into excel. This code only allows me to export one table. Also, how can I display a save prompt dialog?

protected void export_Click(object sender, EventArgs e)
{
string sql = null;
string data = null;
string path = save_as.Text;
int i = 0;
int j = 0;
Excel.Application xlApp;
Excel.Workbook xlWorkBook;
Excel.Worksheet xlWorkSheet;
object misValue = System.Reflection.Missing.Value;
xlApp = new Excel.ApplicationClass();
xlWorkBook = xlApp.Workbooks.Add(misValue);
xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);
//connectionString = "data source=servername;initial catalog=databasename;user id=username;password=password;";
SqlConnection cnn = new SqlConnection(GetConnectionString());
cnn.Open();
sql = "SELECT Story, CreationDate FROM Story";
SqlDataAdapter dscmd = new SqlDataAdapter(sql, cnn);
DataSet ds = new DataSet();
dscmd.Fill(ds);
for (i = 0; i <= ds.Tables[0].Rows.Count - 1; i++)
{
for (j = 0; j <= ds.Tables[0].Columns.Count - 1; j++)
{
data = ds.Tables[0].Rows[i].ItemArray[j].ToString();
xlWorkSheet.Cells[i + 1, j + 1] = data;
}
}
xlWorkBook.SaveAs(path+".xls", Excel.XlFileFormat.xlWorkbookNormal, misValue, misValue, misValue, misValue, Excel.XlSaveAsAccessMode.xlExclusive, misValue, misValue, misValue, misValue, misValue);
xlWorkBook.Close(true, misValue, misValue);
xlApp.Quit();
releaseObject(xlWorkSheet);
releaseObject(xlWorkBook);
releaseObject(xlApp);
//MessageBox.Show("Excel file created , you can find the file c:\csharp.net-informations.xls");
}
private void releaseObject(object obj)
{
try
{
System.Runtime.InteropServices.Marshal.ReleaseComObject(obj);
obj = null;
}
catch (Exception ex)
{
obj = null;
//MessageBox.Show("Exception Occured while releasing object " + ex.ToString());
}
finally
{
GC.Collect();
}
}