ALTER TABLE prestations
  ADD COLUMN IF NOT EXISTS formats TEXT[] NOT NULL DEFAULT '{}';

UPDATE prestations
SET formats = CASE
  WHEN format IS NOT NULL THEN ARRAY[format::text]
  ELSE '{}'
END
WHERE formats IS NULL OR cardinality(formats) = 0;

ALTER TABLE reservations
  ADD COLUMN IF NOT EXISTS format_reservation TEXT;

UPDATE reservations AS r
SET format_reservation = p.format::text
FROM prestations p
WHERE r.prestation_id = p.id
  AND r.format_reservation IS NULL
  AND p.format IS NOT NULL;