带有 ORDER BY CASE 子句的范围无法正常工作

Question

我的 rails 模型上有一个范围，可以帮助我对对象进行分类。如下所示：

scope :active, ->(u = nil, now = "NOW()") {
  published_and_private(u).eager_load(:images)
    .where("(listing = 1 AND complete = 0) OR " +                                        # LISTING
         "(online_only = 1 AND scheduled_end_time + INTERVAL 1 DAY >= #{now}) OR " +   # TIMED
         "(online_only = 0 AND listing = 0 AND starts_at + INTERVAL 1 DAY >= #{now})") # LIVE
    .order("complete, CASE WHEN sort_index IS NOT NULL THEN sort_index " +
         "WHEN scheduled_end_time IS NOT NULL THEN scheduled_end_time " +
         "WHEN starts_at IS NOT NULL THEN starts_at ELSE #{now} + INTERVAL 10 YEAR END")
}

下面是查询得到运行时返回的数据库中的数据：

select id, name, complete, sort_index, starts_at, scheduled_end_time from auctions where published = 1 ORDER BY complete, CASE WHEN sort_index IS not NULL THEN sort_index WHEN scheduled_end_time IS NOT NULL THEN scheduled_end_time WHEN starts_at IS NOT NULL THEN starts_at ELSE (NOW() + INTERVAL 10 YEAR) END;


+----+-----------------------------------+----------+------------+---------------------+---------------------+
| id | name                              | complete | sort_index | starts_at           | scheduled_end_time  |
+----+-----------------------------------+----------+------------+---------------------+---------------------+
| 21 | Listing: Mountain Cabin Estate    |        0 |          1 | NULL                | NULL                |
| 17 | Multi-Item Online Only            |        0 |          2 | 2017-08-07 06:48:00 | 2017-08-21 12:48:00 |
|  9 | Multi-item Live Auction           |        0 |       NULL | 2017-08-21 18:48:02 | NULL                |
| 19 | Many Item LIVE Auction            |        0 |       NULL | 2017-08-21 18:48:02 | NULL                |
| 10 | Single Item Online Only           |        0 |       NULL | 2017-08-07 18:48:03 | 2017-08-22 00:48:02 |
| 18 | MANY Item Timed Auction           |        0 |       NULL | 2017-08-07 18:48:03 | 2017-08-22 00:48:02 |
| 22 | LISTING: Multi-parcel Real Estate |        0 |       NULL | NULL                | NULL                |
| 20 | Bad Images                        |        0 |          3 | 2017-08-21 14:48:00 | NULL                |
|  8 | Single Item Live Auction          |        1 |       NULL | 2017-08-21 18:48:02 | NULL                |
+----+-----------------------------------+----------+------------+---------------------+---------------------+

我的问题是排序索引为 3 的对象不合适，任何超过 2 的数字都会发生这种情况，我完全不知道为什么会这样。我期望查询将该对象放在 sort_index 为 2.

的那个对象的正下方

如有任何帮助、指导或见解，我们将不胜感激。

Answer 1

你能试试用 ISNULL 代替吗，例如：

.order("complete, ISNULL(sort_index), sort_index, " +
         "ISNULL(scheduled_end_time), scheduled_end_time " +
         "ISNULL(starts_at), starts_at")

Answer 2

无法将所有这些条件放入 CASE... WHEN。 CASE ... WHEN 在 WHERE 子句中有效地创建了一个伪列。所以你所做的没有什么不同：

SELECT *, CASE /* your logic */ END AS sort_logic 
/* 
   Notice that the sort_logic column doesn't actually exist in the table. Instead
   MySQL calculates the value and for the duration of this query
*/
WHERE /* <stuff> */
ORDER BY sort_logic

您真正想要的是一系列列值。 @Darshan 上面有一种方法，基本上是创建一系列布尔列并将它们添加到排序中：

complete, ISNULL(sort_index) DESC, 
          /*
             Desc and ASC are important here. You want NOT NULL values to float to
             the top, but you want the columns to work in ascending order.
          */
          sort_index ASC, 
          ISNULL(scheduled_end_time) DESC, scheduled_end_time ASC, 
          ISNULL(starts_at) DESC, starts_at ASC,

您还可以选择将列值默认为 MySQL 最大值。在这种情况下 '9999-12-31' 表示 highest possible date, and ~0 represents the max int value:

complete, 
   ISNULL(sort_index, ~0), 
   ISNULL(scheduled_end_time, '9999-12-31'), 
   ISNULL(starts_at, '9999-12-31')

在这种情况下，逻辑是 "Sort by complete, if sort_index isn't null use that for sorting, otherwise throw the result to the end of the list where sort_index isn't null…"，所有其他列也遵循相同的逻辑。

Answer 3

您要查找的订单子句可能是：

order by complete,
         Coalesce(
           sort_index,
           scheduled_end_time,
           starts_at,
           #{now} + INTERVAL 10 YEAR
         )

但是，您正在将整数与此类日期进行比较，所以我不确定它是如何工作的——可能是通过隐式类型转换，这不太可能导致预期的结果。

也许你的意思是：

order by complete,
         sort_index,
         Coalesce(
           scheduled_end_time,
           starts_at,
           #{now} + INTERVAL 10 YEAR
         )

Answer 4

最后尝试使用 -value 技巧对 NULL 进行排序。我也像其他人一样添加了合并，这确实清理了该 case 语句。

ORDER BY 
  complete, 
  -sort_index DESC, -- Sort ascending with nulls last
  COALESCE(scheduled_end_time, starts_at, now() + INTERVAL 10 YEAR)
;

你也可以查看我的sqlfiddle

带有 ORDER BY CASE 子句的范围无法正常工作

Scope with ORDER BY CASE clause not working properly

mysql

named-scope

ruby-on-rails