title: How to make the system realize that the RFID card is read for 2nd time for sign out?
body: <p>I am a beginner and I need some help/guidance! 
  So basically I am trying to make an attendance system using Raspberry Pi 4 and RFID reader and writer. So far, everything is working well but I am struggling with sending data for sign_out. For now, the same timestamp that is in sign_in get marked in signed_out in the database also, but here I would like to make that when the RFID card is read for the 2nd time the data get filled in sign_out column. 
  If you have any other suggestion I will happy to hear/learn, thanks.
  EDIT: "the whole code was deleted from this question"</p>