i'm experiencing a weird behavior with winform c# timer

i'm trying to update datagridview from sql server database using a timer. First i got 2 strings

string pervCount = "0";
string newCount = "0";

they are out of my timer, the rest is inside the timer (edit1)
then i'm counting the rows in my sql table using:

            conn.Open();
            SqlCommand cmd = new SqlCommand("SELECT COUNT(InvoiceID) FROM InvoicesHeaderTable;", conn);
            SqlDataReader dr = cmd.ExecuteReader();
            while (dr.Read())
            {
                newCount = dr.GetValue(0).ToString();
            }
            conn.Close();

then i'm checking:

            if (pervCount != newCount)
            {
                conn.Open();
                SqlCommand cmd1 = new SqlCommand("select InvoiceID, CustomerName,TotalInvoicePrice from InvoicesHeaderTable where CompleteStatus=0", conn);
                SqlDataAdapter da = new SqlDataAdapter(cmd1);
                DataTable dt = new DataTable();
                da.Fill(dt);
                if (dt.Rows.Count > 0)
                {
                    CashierDgv.DataSource = dt;
                }
                conn.Close();
                pervCount = newCount;
            }

the if statement should not work since pervCount = newCount since i'm a assigning both variables to be equal int the if statement. But some how my datagridview is constantly refreshed.

i used a simpler code that fixed my problem and did exactly what i want.

int pervCount = 0;

out of my timer, then inside my timer:

            SqlCommand cmd = new SqlCommand("SELECT InvoiceID,CustomerName,TotalInvoicePrice FROM InvoicesHeaderTable where CompleteStatus =0", conn);
            SqlDataAdapter adab = new SqlDataAdapter(cmd);
            DataTable table = new DataTable();
            adab.Fill(table);
            if (table.Rows.Count > pervCount)
            {
                CashierDgv.DataSource = table;
                pervCount = table.Rows.Count;
            }