用同一表中同一列的值更新列

对同一个表使用带有联接的更新。如果我误解您需要在最后两行中切换“t”和“f”,则此查询将更新sald='t'处的行。

UPDATE product AS p 
SET uuid = p2.uuid
FROM product p2
WHERE p2.product_id = p.product_id
  AND (p2.variant_id = p.variant_id  OR p2.variant_id IS NULL OR p.variant_id IS NULL)
  AND p.sold = 't'
  AND p2.sold = 'f'

db-fiddle

我想没有理由 product_id 和 variant_id 两者兼而有之 NULL :

update product p1 set uuid = p2.uuid from product p2
where p1.sold = 't' and p2.sold = 'f'
  and (
    (p2.product_id = p1.product_id and p2.variant_id = p1.variant_id)
    or
    (p2.product_id IS NULL and p2.variant_id = p1.variant_id)
    or
    (p2.product_id = p1.product_id and p2.variant_id IS NULL)
  )