[jamesmstone]

pre postgres 15 can you solve this with two unique constraints ?

unique (EmployeeName), unique (EmployeeName, CarID)

[masklinn]

You’d most likely solve this by making the CarID NOT NULL because there’s why would you even have a row with no useful data?

And if this is your employee table, you’d have UNIQUE (EmployeeData) and UNIQUE (CarID), and it would do what you want.

[ryanbrunner]

That's not quite the same, since the previous solution of unique (EmployeeName, CarID) allowed for one employee to have 2 separate cars. You have to use conditional indexes to solve this.