SELECT p.id, p.name, s.id AS id_sklad, s.delivery_time, p2s.price, p2s.cnt FROM products p
LEFT JOIN product_to_sklad p2s ON (p.id = p2s.id_product) 
LEFT JOIN sklads s ON (s.id = p2s.id_sklad)
WHERE if (
p2s.cnt >=4,
s.delivery_time = (SELECT min(s2.delivery_time) FROM sklads s2 
        LEFT JOIN product_to_sklad p2s2 ON (s2.id = p2s2.id_sklad) 
        WHERE p2s2.id_product = p.id),
p2s.cnt = (SELECT max(p2s3.cnt) FROM product_to_sklad p2s3
        WHERE p2s3.id_product = p.id) 
        AND s.delivery_time = (
                SELECT min(s4.delivery_time) FROM sklads s4
                LEFT JOIN product_to_sklad p2s4 ON (s4.id = p2s4.id_sklad)
                WHERE p2s4.id_product = p.id)
)

SELECT p.name, cte.id_sklad, s.delivery_time, ps.price, ps.cnt `count`
FROM products p
LEFT JOIN (SELECT DISTINCT
       ps.id_product,
       CASE WHEN SUM(ps.cnt>=4) OVER (PARTITION BY ps.id_product) >0
            THEN FIRST_VALUE(ps.id_sklad) OVER (PARTITION BY ps.id_product
                                                ORDER BY ps.cnt<4,
                                                         s.delivery_time ASC, 
                                                         s.name ASC) 
            ELSE FIRST_VALUE(ps.id_sklad) OVER (PARTITION BY ps.id_product
                                                ORDER BY ps.cnt DESC, 
                                                         s.delivery_time ASC, 
                                                         s.name ASC)
            END id_sklad
FROM product_to_sklad ps, sklads s
WHERE ps.id_sklad = s.id
) cte
LEFT JOIN cte ON p.id = cte.id_product
LEFT JOIN sklads s ON s.id = cte.id_sklad
LEFT JOIN product_to_sklad ps ON (ps.id_product, ps.id_sklad) = (cte.id_product, cte.id_sklad)

 OVER (PARTITION BY ps.id_product)