I have two fields, serial_no and vehicle_id and I want to say if the serial_no is empty then the vehicle_id has to be 17 characters long, but if there is something in the serial_no then don't worry about the vehicle_id.

I wrote:

case(serial_no = " ", length(vehicle_id)=17)

but it doesn't work because whether or not there is something in serial_no it still comes up saying I need something in the vehicle_id.

How would I fix this?

Do you mean that if there is something in the Serial ID then you:

a. still need a vehicle ID but length doesn't matter, or

b. don't need a vehicle ID at all?

You can do both of these by validating the vehicle_id field.

For A:

(IsEmpty(serial_no) and Length(vehicle_id) = 17) or

(not IsEmpty(serial_no) and IsEmpty(vehicle_id))

For B:

(IsEmpty(serial_no) and Length(vehicle_id) = 17) or

(not IsEmpty(serial_no) and not IsEmpty(vehicle_id))

Then show an appropriate validation message like:

"If the serial number is empty, then your vehicle id must be 17 characters long.

If you have entered a serial number... etc etc"

Thanks so much Russ that's exactly what I needed.