mysql - 有条件地更改 SQL 中的排序方向

Question

我对 a similar question that was asked many years ago on StackOverflow 有一个有趣的看法

为简单起见，假设我有一个包含三列的表:

+----+------+-------+
| id | cond | value |
+----+------+-------+
| 1  |  1   |  "A"  |
| 2  |  0   |  "B"  |
| 3  |  1   |  "C"  |
| 4  |  0   |  "D"  |
| 5  |  1   |  "E"  |
+----+------+-------+

现在我想先按 cond 对这个表进行排序，然后按 value ascending if cond 为 0，如果 cond 为 1，则 descending。最终排序表应如下所示:

+----+------+-------+
| id | cond | value |
+----+------+-------+
| 2  |  0   |  "B"  |
| 4  |  0   |  "D"  |
| 5  |  1   |  "E"  |
| 3  |  1   |  "C"  |
| 1  |  1   |  "A"  |
+----+------+-------+

请注意，我不能依赖于 value 为数字，所以我不能做一些聪明的事情，例如:

order by cond, (case when cond = 0 then value else -value end)

Answer 1

使用两个分开的条件 cond 来排序你的结果:

select *
from yourtable
order by 
    cond, 
    case when cond = 0 then `value` else 1 end,
    case when cond = 1 then `value` else 1 end desc

参见 SQLFiddle DEMO 在这里。