By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
Help with an interesting Postgres question: Why isn't an Index Only Scan used on a partition accessed via the parent table?.
CREATE TABLE
INSERT 0 1
INSERT 0 1
CREATE TABLE
CREATE INDEX
ERROR: new row for relation "relationship" violates check constraint "relationship_check" DETAIL: Failing row contains (1, 1, 100).
INSERT 0 1
ERROR: duplicate key value violates unique constraint "unique_pair_ix" DETAIL: Key (LEAST(thing_one, thing_two), GREATEST(thing_one, thing_two))=(1, 2) already exists.