export large datatable data to .csv file in c# windows applications

Count the number of processors. Create a thread for each, and divide the rows over the threads. Have each export to their own file, combine the files at the end. Add a nice progress-display and you're done.

FWIW; a "lac" is not an international recognized amount.

Easy way is to save it in XML and open it in EXCEL.
MSExcel can generate the schema for xml automatically.
Once a file is opened in Excel we can save it in csv.
It may be a crap for you.
But it's really time saving and easy coding.

//code under export button_Click
        var ds = obj.Export();
        dset.WriteXml(@"D:\ExportExcelFiles\sample.xml");
        Label1.Text = @"File Downloaded to D:\ExportExcelFiles\sample.xml";


//Business logic code which is defined under some class..
SqlDataAdapter da = null;
    DataSet ds;
    public DataSet Export()
    {
        string qryString = "Select Category.CategoryName, Category.CategoryID, Item.ItemName, Item.Description, Item.TaxID, Item.HKU From Category Left Join Item ON Category.CategoryID=Item.CategoryID";
        con = new SqlConnection(conString);
        if (con.State == ConnectionState.Closed)
        { con.Open(); }
        cmd = new SqlCommand(qryString, con);
        ds= new DataSet();
        da = new SqlDataAdapter(cmd);
        da.Fill(ds);
        return ds;

    }

Thanks,
Rohith.

Hmmm? Not sure what is going on with the above code and why its posted that way but its creating a Datatable for no reason as it uses this messy joined concatenation of columns from the reader itself later. Also most of the syntax needs correcting.

Not good to paste defective code that doesn't work it distresses others and wastes their time.

A far simpler way is to simply create a Streamreader object and simply iterate through a filled Datatable itself.

using System;
using System.Linq;
using System.Data;
using System.IO;
using System.Data.SqlClient;
using System.Configuration;


namespace ExportSQLTableToExcel
{
    class Program
    {
        static void Main(string[] args)
        {
           
        string ExcelFileName = ConfigurationManager.AppSettings["ExcelFileName"];
        string FolderPath = ConfigurationManager.AppSettings["FolderPath"];
        string ConnectionString = ConfigurationManager.AppSettings["ConnectionString"];
            
            // create the reader 
            SqlConnection sqlConnection1 = new SqlConnection(ConnectionString);
            SqlCommand cmd = new SqlCommand();
            SqlDataReader reader;

            cmd.CommandText = " select *  FROM [dbo].[YourTable]";
            cmd.CommandType = CommandType.Text;
            cmd.Connection = sqlConnection1;

            sqlConnection1.Open();
            reader = cmd.ExecuteReader();

            //Create the datatable

            using (DataTable dt = new DataTable())
            {
                dt.Load(reader);
                Console.WriteLine(dt.Rows.Count);  //check its filled 

                //Create the Streamwriter

                StreamWriter CsvfileWriter = new StreamWriter(@"C:\testfile.csv");

                using (CsvfileWriter)
                {

                    //Use sting join methods to attach and write the columns 
                    CsvfileWriter.WriteLine(string.Join(",", 
                    dt.Columns.Cast<DataColumn>().Select(csvfile => 
                    csvfile.ColumnName)));

                    foreach (DataRow row in dt.Rows)
                    {
                        //Use sting join methods to attach and write and iterate 
                        //through the rows of the datatable
                        CsvfileWriter.WriteLine(string.Join(",", row.ItemArray));
                    }
                }
            }
           
            sqlConnection1.Close();

        }

    }
    
}