在窗体C＃Visual Studio中比较两个日期起始日期和数据库SQL Server中的日期

Question

I want make a auto number based date and number at "Transaction" Form. But i have problem with make a "condition" to compare date "today" and date "yesterday". If date is different, then will make a new "autonumber" from number 1. For example, that date is 2019-08-08 so the ID from "permintaanId" is P2019080803 (two last number is how many transaction make that day). And tomorrow is 2019-08-09 will make ID P2019080901 (two last number will reset because no one transaction make)

private void auto()
   {
       long hitung;
       string urut;
       SqlConnection conn = konn.GetConn();
       conn.Open();
       cmd = new SqlCommand("select permintaanId from permintaan_data where permintaanId in(select max(permintaanId) from permintaan_data) order by permintaanId DESC", conn);
       rd = cmd.ExecuteReader();
       rd.Read();
       if (rd.HasRows) //<- this condition
       {
           hitung = Convert.ToInt64(rd[0].ToString().Substring(rd["permintaanId"].ToString().Length - 2, 2)) + 1;
           string joinstr = "00" + hitung;
           urut = "P" + DateTime.Now.ToString("yyyyMMdd") + joinstr.Substring(joinstr.Length - 2, 2);
       }
       else
       {
           urut = "P" + DateTime.Now.ToString("yyyyMMdd") + "01";
       }
       rd.Close();
       txt_noPermintaan.Text = urut;
       conn.Close();
   }

Answer 1

    DECLARE @permintaanId INT=0
DECLARE @NewNo VARCHAR(40)=''

select @permintaanId=CAST(ISNULL(MAX(RIGHT(permintaanId,1)),0)+1 AS INT)
FROM permintaan_data
WHERE CAST([tranData] AS DATE) =CAST(GETDATE() AS DATE)

SET @NewNo='P'+CONVERT(VARCHAR(10),GETDATE(),112)+CAST(@permintaanId AS VARCHAR(10))

SELECT @NewNo

Answer 2

get last item created

cmd = new SqlCommand("select top1 permintaanId from permintaan_data order by DESC", conn);
rd = cmd.ExecuteReader();

if (rd.HasRows)
{
    var id = rd["the one with p and 2 numbers at the end"].ToString();
    var dateLastCreated = id.ToString().Remove(0,1).Remove(id.Length-2,2);
   if (dateLastCreated == DateTime.Now.ToString("yyyyMMdd"))
   {
       //increment
   }
   else
   {
       //create new
   }

}