Validate that Salesforce field is unique

Is there a way to create a validation that a field is unique?

Say I have a custom field for which seat on my private jet each Contact has - I'd love if there were a way to validate that I hadn't double-assigned that seat.

I haven't found a simple function like ISBLANK to test uniqueness directly, but is there another way to accomplish this?

Thanks!

Solution

I don't beleive there's a way to do it with a validation rule, but the field definition (for most field types) includes the option to mark it as uniuque, just update the field definition.

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