Hello.

I have users that input these data into a form at the same time:

Machine Start Time End Time
user 1 01 1430 1545
user 2 02 1500 1630
user 3 01 1600 1648
etc.

If by mistake user 2 inputs Machine 01 (it's already working)

How do I prevent that data from being stored using the insert sentence ?
There is no primary key to compare user's input.

Thank you.

c.x.