Prevent duplicate recordings

If this column is used as a datetime, how to set it not to duplicate it?

Now is the date of attendance column is date time from the first date is date only.
At first I used The column titled First Name-Last Name Date of Attendance is the key.

using the formula
Valid If formula for colum :
NOT(IN([_THIS], SELECT(Time stamp[employee ID], [attendance date] = TODAY())))

Error_Message_If_Invalid : “You are registered. can’t repost”

But today I tried to repeat it. It did. From the usual studies in this group and groups. It cannot be re-recorded.

Want to record the date of attendance, 1 entry per day per person or code

The main columns are as follows:

  1. Code
  2. Name - Surname
  3. Date of attendance (date time) press enter from user setting and press action save
  4. The date of the event (date time), use the press action to now.

Maybe this instead?

      Time stamp[attendance date],
      ([employee ID] = USEREMAIL())

It can still be recorded repeatedly.

The previous old formula that will use Not-In

“Down time”,
([Date of attendance] <> [_THISROW].[Date of attendance]),
([unique-column] = [_THISROW].[unique-column])