CREATE UNIQUE INDEX name ON table (column [, ...]) [ NULLS [ NOT ] DISTINCT ];

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/17/indexes-unique.html
Description:

This says it works from 12 onwards but actually from 15 onwards
Prior to 15 unique partial indexes needed creating, e.g. (parent_ID, NAME)
where parent_ID is not null and (NAME) where parent_id is null