In this C# Gist, a CsvHelper.CsvWriter is used to asynchronously write the results of a SQL query to a CSV file without worrying about each column's data type.

SqlDataReader_To_CSV_Using_CsvHelper_Library.cs

try
{
    await using var sqlDataReader = await sqlCommand.ExecuteReaderAsync(cancellationToken);
    await using var streamWriter = new StreamWriter($"{reportName}_{startDate:dd-MM-yyyy}-{endDate:dd-MM-yyyy}.csv");
    await using var csvWriter = new CsvWriter(streamWriter, _csvConfiguration);

    var columnSchema = sqlDataReader.GetColumnSchema();
    var columnCount = columnSchema.Count;

    // write headers to CSV:
    foreach (var columnName in columnSchema.Select(column => column.ColumnName))
    {
        csvWriter.WriteField(columnName);
    }

    await csvWriter.NextRecordAsync();

    // write rows to CSV:
    while (await sqlDataReader.ReadAsync(cancellationToken))
    {
        object[] values = new object[columnCount];
        sqlDataReader.GetValues(values);
        foreach (var v in values)
        {
            csvWriter.WriteField(v);
        }
        await csvWriter.NextRecordAsync();
    }

    if (streamWriter.BaseStream is FileStream fs)
    {
        _logger.LogInformation("Wrote report file at {0}", fs.Name);
    }
}
catch (Exception e)
{
    _logger.LogError("Error during reading SQL data and writing CSV files: {0}", GetExceptionMessageFirstLine(e));
}

Very useful, thank you