Yes. A `UNIQUE` constraint is implemented with the help of a unique index - a b-tree index with default sort ordering over all involved columns. The index is created and maintained automatically, and is used for all purposes like a plain unique index by Postgres.

There is no need to create another (redundant) unique index like it, that would be a waste of resources.

Detailed explanation:

- [How does PostgreSQL enforce the UNIQUE constraint / what type of index does it use?][1]
- https://dba.stackexchange.com/questions/90722/is-unique-index-better-than-unique-constraint-when-an-index-with-an-operator-cla/90810#90810


 [1]: https://stackoverflow.com/a/9067108/939860