For Postgres specific approach, you may refer to https://blog.rustprooflabs.com/2022/07/postgres-15-unique-improvement-with-null https://blog.rustprooflabs.com

For Postgres specific approach, you may refer to https://blog.rustprooflabs.com/2022/07/postgres-15-unique-improvement-with-null https://blog.rustprooflabs.com/2022/07/postgres-15-unique-im... Practically speaking, I go with not null, and always set default value.