Question

我正在使用下面的SQL从两个MySQL数据库表中获取每周的价格历史记录：

SELECT ROUND(MIN(ph.price), 0) AS min_price, WEEK(ph.added) AS added
FROM products_data pd JOIN products_history ph ON pd.id = ph.product_id
WHERE ph.price > 0
GROUP BY added
ORDER BY added

一切都很好，除了products_history表仅包含更改价格后的条目。

如果一周A的价格变动造成一周A的最低min_price，那么一切都很好。

但是，如果价格变化发生在A周之前的1周以上，则该查询未检测到价格变化，因此，获取的A周最低价min_price可能不正确：（

例如，现在发生的事情：

Week 13: Price change so min_price for product A = 4.78,
query returns 4.78 (correct)

Week 14: Price change so min_price for product B = 4.74,
query returns 4.74 (correct)

Week 15: Price change so min_price for product C = 4.79,
query returns 4.79 (wrong, should be 4.74 since that's still the price for product B)

Week 16: Price change so min_price for product C = 4.75,
query returns 4.75 (wrong, should be 4.74 since that's still the price for product B)

Week 17: No price changes,
query returns nothing...  (wrong, should be 4.74 since that's still the price for product B)

Week 18: Price change so min_price for product B = 4.77,
query returns 4.77 (wrong, should be 4.75 since that's still the price for product C)

关于如何使查询每周检索最低的最低价格的任何想法，即使更改较早发生？

products_data具有以下列：

id, name, category
2434, 'Product A', 'Bits'
3437, 'Product B', 'Bits'

products_history具有以下列：

id, product_id, price, added
4311, 2434, 4.74, 2019-05-15 22:19:50
2434, 3437, 4.78, 2019-05-15 22:19:59

工作版本基于以下Gordon Linoff的正确答案：

SELECT id, yw.yyyyww,
       (SELECT ph2.price
        FROM products_history ph2
        WHERE ph2.price > 0 AND
              YEARWEEK(ph2.added) <= yw.yyyyww AND ph2.product_id = pd.id
        ORDER BY YEARWEEK(ph2.added) DESC,  -- put the most recent values first
                 ph2.price ASC  -- by lowest price
        LIMIT 1
       ) AS min_price
FROM products_data pd CROSS JOIN
     (SELECT DISTINCT YEARWEEK(ph.added) AS yyyyww
      FROM products_history ph
     ) yw

Answer 1

如果我的理解正确，那么您希望每个星期的每种产品都具有价值。如果是这样，请使用cross join生成行，然后-在MySQL中-您可以使用相关子查询来获取价格

SELECT product_id, yw.yyyyww,
       (SELECT ph2.price
        FROM products_history ph2
        WHERE ph2.price > 0 AND
              YEARWEEK(ph2.added) <= yw.yyyyww
        ORDER BY YEARWEEK(ph2.added) DESC,  -- put the most recent values first
                 ph2.price ASC  -- by lowest price
       ) as min_price
FROM products_data pd CROSS JOIN
     (SELECT DISTINCT YEARWEEK(ph.added) as yyyyww
      FROM products_history ph
     ) yw

MySQL，选择包括前几周

1 个答案: