Re: There can be only one

Andreas Kretschmer <andreas(at)a-kretschmer(dot)de> wrote:

> Create a partial unique index on is_default.

as an example:

test=# CREATE TABLE payment_via (
id int PRIMARY KEY,
provider text NOT NULL,
keys hstore NOT NULL DEFAULT '',
is_default boolean NOT NULL DEFAULT FALSE
);
CREATE TABLE
test=*# create unique index idx_default on payment_via(is_default) where
is_default;
CREATE INDEX
test=*# insert into payment_via values (1, 'foo','', true);
INSERT 0 1
test=*# insert into payment_via values (2, 'bla','', false);
INSERT 0 1
test=*# insert into payment_via values (3, 'blubb','', true);
ERROR: duplicate key value violates unique constraint "idx_default"
DETAIL: Key (is_default)=(t) already exists.
test=*#

Andreas
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