Question

我有一张桌子“产品”，我每天都有产品价格，现在我想知道昨天出现的产品哪些是昨天出现的产品，如果两天都存在，那么什么是价格变化的差异。

例如表“产品”：

locale     productID        price         date
US         pro1             100           2015-04-02
US         pro2             200           2015-04-02
CA         pro1             100           2015-04-02

US         pro1             110           2015-04-01
US         pro3             500           2015-04-01
CA         pro4             100           2015-04-01

所以期望的输出应该是： -

locale_t|productID_t|price_t|date_t|locale_y|productID_y|price_y|date_y|change
US       pro1        100   2015-04-02  US    pro1        110   2015-04-01   10
US       pro2        200   2015-04-02        REMOVED                       200
         REMOVED                       US    pro3        500   2015-04-01  500
CA       pro1        100   2015-04-02        REMOVED                       100
         REMOVED                       CA    pro4        100               100

其中locale_t表示locale_today，locale_y表示locale_yesterday。所以我可以清楚地告诉我们昨天删除了多少产品以及今天增加了多少产品。

Answer 1

你想要一个自我交叉连接，但是你真的加入了两个不同的子集，这很复杂。

为实现这一点，一种方法是在同一数据上连接两个子查询，例如： http://sqlfiddle.com/#!15/2d6ae/15：

SELECT 
  coalesce(yesterday.locale, today.locale) AS locale,
  coalesce(yesterday."productID", today."productID") AS "productID",
  today.date AS date_t,
  today.price AS price_t,
  yesterday.date AS date_y,
  yesterday.price AS price_y,
  today.price - yesterday.price AS "change"
FROM (
    SELECT * FROM Table1 WHERE "date" = '2015-04-01'
  ) AS yesterday
  FULL OUTER JOIN (
    SELECT * FROM Table1 WHERE "date" = '2015-04-02'
  ) AS today
  ON (today."locale" = yesterday."locale"
      AND today."productID" = yesterday."productID")
 ORDER BY 1, 2;

 locale | productID |   date_t   | price_t |   date_y   | price_y | change 
--------+-----------+------------+---------+------------+---------+--------
 CA     | pro1      | 2015-04-02 |     100 |            |         |       
 CA     | pro4      |            |         | 2015-04-01 |     100 |       
 US     | pro1      | 2015-04-02 |     100 | 2015-04-01 |     110 |    -10
 US     | pro2      | 2015-04-02 |     200 |            |         |       
 US     | pro3      |            |         | 2015-04-01 |     500 |       
(5 rows)

预期的结果并不完全相同，但你并没有真正尝试用文字指明你想要什么，我不想猜测。

我怀疑您可能希望在coalesce列中使用change来生成null结果，例如：

coalesce(today.price - yesterday.price, today.price, -yesterday.price) AS "change"

如何加入同一张桌子以获得两天之间的价格差异？

1 个答案: