Optimization c# datatable.. help...Please

Question

Hi i have a function of which iterates through a data table and constructs the output of a table to SQL format.

i.e Col 1, Col2, Col3, Row1, Row2, Row3 Outputs to INSERT INTO *tablename*(Col1, Col2, Col2)VALUES('Row1','Row2','Row3') 

 

If the datatable is loaded with a small amount of rows the processing speed per row is fast. i.e if i load 200 rows it's instant.

 

But if I loaded 10,000 rows its 2-3 seconds per row, can you help optimize please?

 

Here is my function

 

public string sqlconstructorForOutputofCSVandReturnTEXT(string sCommand)

{

string concat = "";

using (DataTable dt = new DataTable())

{

StringBuilder sb = new StringBuilder();

using (StreamWriter sw = new StreamWriter(textBox2.Text))

{

using (SqlConnection sqlConnection = new SqlConnection(connectionString))

{

sqlConnection.Open();

SqlCommand sqlCommand = new SqlCommand(sCommand, sqlConnection);

SqlDataAdapter adapter = new SqlDataAdapter(sqlCommand);

adapter.Fill(dt);

string[] columnnames = dt.Columns.Cast<DataColumn>().Select(x => x.ColumnName).ToArray();

dt.Columns.Add("SQL");

dt.Columns["SQL"].SetOrdinal(0);

foreach (string colu in columnnames)

if (colu == "SQL")

{

}

else

concat = String.Format("{0}{1},", concat, colu);

string d = concat.Remove(concat.Length - 1, 1);

int rowcount = 0;

foreach (DataRow row in dt.Rows)

{

foreach (DataColumn col in dt.Columns)

{

for (int i = 0; i < dt.Rows.Count; i++)

dt.Rows[i]["SQL"] = String.Format("INSERT INTO {0} ({1})VALUES(", listBox1.SelectedItem, d);

if (col.ColumnName == "SQL")

sb.AppendFormat(String.Format("{0}", row[col]));

else

sb.AppendFormat(String.Format("'{0}',", row[col]));

}

sb.Remove(sb.Length - 1, 1);

sb.AppendLine(")");

rowcount = rowcount + 1;

Text = rowcount.ToString();

}

sw.WriteLine(sb);

return sb.ToString();

; ;

}

}

}

}