How to make sure there is no duplicate user entry?

I need to make a column "Unique" in a table so that there is not duplicate entry. How can I do that?

You can hack the Now() function to give you something pretty close to unique, if you’re not worried about multiple users submitting at the same time. That’s pretty fast to setup.

Or, you can create an table that just holds a number. Then create an automation that writes that number into each new row in your table, and then increments the number by one.