Postgres 13

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CREATE TEMP TABLE order_splits_config (
id                   int,
pair_id              int
);

CREATE TEMP TABLE active_pairs (
id                  int,
pair                varchar(30),
exchange_active     boolean,
exchange_id         int
);

INSERT INTO order_splits_config(id, pair_id) VALUES
  (1, 83)
, (2, 58)
, (34, 34)
;

INSERT INTO active_pairs(id, pair, exchange_active, exchange_id) VALUES
  (1, 'US/EN', TRUE, 2)
, (2, 'GB/UK', TRUE, 3)
, (2, 'FR/EU', TRUE, 4)
;
3 rows affected

3 rows affected

-- pair defined UNIQUE
SELECT id, pair, exchange_id
FROM   active_pairs b
WHERE  NOT EXISTS (SELECT FROM order_splits_config a WHERE a.pair_id = b.id);


id
pair
exchange_id


1
US/EN
2

2
GB/UK
3

2
FR/EU
4


-- pair not UNIQUE
SELECT DISTINCT ON (pair)
       id, pair, exchange_id
FROM   active_pairs b
WHERE  NOT EXISTS (SELECT FROM order_splits_config a WHERE a.pair_id = b.id);


id
pair
exchange_id


2
FR/EU
4

2
GB/UK
3

1
US/EN
2