Fauna has an interesting approach to null that I've grown to like:
Null is a real value that can be compared intuitively like any other value (`Equals(null, null)` returns true). [1]
However, in indexes, any term that evaluates to null is simply not stored in the index. So we can create a unique index with multiple null values because they simply won't exist in the index, so won't violate the unique constraint.
If we do care about null values in a particular index, we can handle that by mapping the null value into another value that will get stored in indexes using a "binding", and then use that index to query for or constrain uniqueness by that mapped value [2].
This is not the most convenient thing in the world, but at the end of the day, it feels like an edge case, so I'm happy with having to jump through some hoops to handle it in exchange for making the much more common cases (null comparisons and unique indexes with nullable values) more intuitive and less error prone.
Null is a real value that can be compared intuitively like any other value (`Equals(null, null)` returns true). [1]
However, in indexes, any term that evaluates to null is simply not stored in the index. So we can create a unique index with multiple null values because they simply won't exist in the index, so won't violate the unique constraint.
If we do care about null values in a particular index, we can handle that by mapping the null value into another value that will get stored in indexes using a "binding", and then use that index to query for or constrain uniqueness by that mapped value [2].
This is not the most convenient thing in the world, but at the end of the day, it feels like an edge case, so I'm happy with having to jump through some hoops to handle it in exchange for making the much more common cases (null comparisons and unique indexes with nullable values) more intuitive and less error prone.
[1] https://fauna.com/blog/understanding-nothing-or-null-in-faun...
[2] https://docs.fauna.com/fauna/current/learn/cookbook/fql/sear...