I'm currently coding a mini payroll system for a software engineering subject.

The main thing needed for payroll though is the time, because we all know this is where the salary of the employee will be based upon.

Having this in mind, a payroll software needs to have a table in the database where it can store the time in and the time out of an employee.

I wanted to know if it is possible to apply a constraint on the log in button? It can only be pressed one time and cannot be pressed again until the employee logs out.

Thanks in advance for anyone who can help me