How to insert another table data from select query for exist table - ms-access-2007

Question

Actually I'm creating one database application where if person first day login then his sales_count will be 1, same person login again then its sales_count will be 2 , same user login next day then its sales_count again 1.
For this I created two tables Login and Sales_Details. In Login I have:
User_name, Password and Unique no.
Now, in sales_details I want to fetch only User_name,Unique_no from login detail but at same time I want to increment sales_count in sales_details table also update today date.
Sales_details has
Sales_id,User_name,Unique_No,Sales_count,To_Date field
Actually I tried but nothing happen if To_date is null then insert today date+sales_count as 1 in sales_details
Below I'm pasting my whole code:
string todaydate = DateTime.Now.ToString("dd/MM/yyyy");
string access = "select To_Date from Sales_Details";
cmd = new OleDbCommand(access, con);
con.Open();
using (OleDbDataReader read = cmd.ExecuteReader()){
while (read.Read()){
string date2 = read["To_Date"].ToString();
if (todaydate == date2){
cmd = new OleDbCommand("update Sales_Details set Sales_count= IIF(IsNull(Sales_count), 0, Sales_count) + 1, [To_Date]=Date() where [Unique_No]=#Unique_No", con);
cmd.Parameters.AddWithValue("#Unique_No", txtinput.Text);
con.Open();
int n = cmd.ExecuteNonQuery();
if (n == 0) {
MessageBox.Show("Invalid Unique No.");
} else {
this.DialogResult = DialogResult.OK;
}
con.Close();
} else {
int counter=1;
cmd = new OleDbCommand("insert into Sales_Details select User_name,Unique_No from Login where Unique_No=#Unique_No Union select ISNULL(Sales_Count+1,0) as [#Sales_Count],DATE() AS [To_date]", con);
cmd.Parameters.AddWithValue("#Unique_No", txtinput.Text);
cmd.Parameters.AddWithValue("#Sales_count",counter);
int n1 = cmd.ExecuteNonQuery();
if (n1 == 0){
MessageBox.Show("Invalid Unique No.");
} else {
this.DialogResult = DialogResult.OK;
}
}
}
}
con.Close();