Is there a way for extracting an Excel file from an ado.net query and adding custom columns to it using c#

Question

I have an Excel file template, and I need to extract the data from a SQL Server database to this Excel file using C# as same as the template file.

The problem is that I need to add another column using C# to the Excel file, to make this extracted file look like the template file.

So I will not extract the Excel file's data from my web-form application directly. I need to add some additional columns first.

Answer 1

Convert SQL to CSV while writing SQL result add your custom column data as well. CSV will open in excel by default.

private void SQLToCSV(string query, string Filename)
    {

        SqlConnection conn = new SqlConnection(connection);
        conn.Open();
        SqlCommand cmd = new SqlCommand(query, conn);
        SqlDataReader result = cmd.ExecuteReader();

        using (System.IO.StreamWriter fs = new System.IO.StreamWriter(Filename))
        {
            // Loop through the fields and add headers
            for (int i = 0; i < result.FieldCount; i++)
            {
                string colval = result.GetColumnName(i);
                if (colval.Contains(","))
                    colval = "\"" + colval + "\"";

                fs.Write(colval + ",");
            }

    //CONCATENATE THE COLUMNS YOU WANT TO ADD IN RESULT HERE

            fs.WriteLine();

           // Loop through the rows and output the data
            while (result.Read())
            {
                for (int i = 0; i < result.FieldCount; i++)
                {
                    string value = result[i].ToString();
                    if (value.Contains(","))
                        value = "\"" + value + "\"";

                    fs.Write(value + ",");
                }
                fs.WriteLine();
            }

            fs.Close();
        }
    }

You can covert csv to excel

using Excel = Microsoft.Office.Interop.Excel;

private void Convert_CSV_To_Excel()
{

    // Rename .csv To .xls
    System.IO.File.Move(@"d:\Test.csv", @"d:\Test.csv.xls");

    var _app = new Excel.Application();
    var _workbooks = _app.Workbooks;

    _workbooks.OpenText("Test.csv.xls",
                             DataType: Excel.XlTextParsingType.xlDelimited,
                             TextQualifier: Excel.XlTextQualifier.xlTextQualifierNone,
                             ConsecutiveDelimiter: true,
                             Semicolon: true);

    // Convert To Excle 97 / 2003
    _workbooks[1].SaveAs("NewTest.xls", Excel.XlFileFormat.xlExcel5);

    _workbooks.Close();
}