how to update the qty column in datagridview in c#.

Question

 

 when i call this function only one colum has been updated couln't updated more than one colum

please help me 

 

 public void updatedb()

{

for (int row = 0; row < dataGridView1.Rows.Count - 1; row++)

{

string itmno = dataGridView1.Rows[row].Cells[1].Value.ToString();

string itmqty = dataGridView1.Rows[row].Cells[3].Value.ToString();

// string t = "select * from products where id=" + itmno + "";

// Connnew.DbSearch(t);

con.Close();

MySqlCommand scmd = new MySqlCommand();

scmd.Connection = con;

scmd.CommandText = "select * from products where id in" + itmno + "";

con.Open();

MySqlDataReader dr;

dr = scmd.ExecuteReader();

string oldqty = "", newqty = "";

while (dr.Read())

{

oldqty = dr[5].ToString();

newqty = (int.Parse(oldqty) - int.Parse(itmqty)).ToString();

}

string t2 = ("UPDATE products SET qty = '" + newqty + "' WHERE id = '" + itmno + "' ");

con.Close();

con.Open();

MySqlCommand upcmd = new MySqlCommand(t2,con);

upcmd.ExecuteNonQuery();

MessageBox.Show("Updateeeeeeeeeeeeeeeeeeeeee");

}

con.Close();