How to ensure only a single row with a certain value

Question

Given this table:

CREATE TABLE rollouts
(
    id           UUID        PRIMARY KEY DEFAULT gen_random_uuid(),
    device_id    TEXT        NOT NULL,
    is_active    BOOLEAN     NOT NULL DEFAULT FALSE
);

How can I ensure that for a given device_id, there is only ever one active rollout? Multiple inactive ones are fine, so a simple unique index doesn't cut it.

Answer 1

You can use a partial unique index:

create unique index on rollouts (device_id) 
where is_active;