Scope with ORDER BY CASE clause not working properly

Question

I have a scope on my rails model that is supposed to help me sort my objects. This is shown below:

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")
}

Below is the data from the database that is returned when the query gets ran:

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                |
+----+-----------------------------------+----------+------------+---------------------+---------------------+

My problem is that the object with a sort index of 3 is out of place, this happens for any number over 2 and I am at a complete loss as to why this may be. I was expecting the query to place that object right under the one with a sort_index of 2.

Any help, guidance, or insight would be greatly appreciated.

Answer 1

There isn't a way to put all of those conditions into a CASE... WHEN. CASE ... WHEN effectively creates one pseudo-column in your WHERE clause. So what you did is no different from:

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

What you really want is a series of column values. @Darshan has one approach above, which is basically create a series of boolean columns and add those to the sort:

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, 

You also have the option of defaulting the column values to MySQL max values. In this case '9999-12-31' represents the 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')

In this case, the logic is "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…" and the same logic follows for all of the other columns.

Answer 2

Could you try with ISNULL instead, e.g.:

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

Answer 3

Possibly the order clause you're looking for is:

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

However, you're comparing an integer with dates in this sort, so I'm not sure how that is going to work -- possibly through an implicit type cast, which is unlikely to lead to the desired result.

Maybe you mean:

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

Answer 4

Try sorting NULLs last using the -value trick. I've added coalescing, too, as have others, which really cleans up that case statement.

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

You can also check my sqlfiddle