MySQL GROUP BY和COUNT over Multiple Columns

Question

我有一個MySQL表如下：

+----+-------+-------+-------+-------+-------+
| ID |  MON  |  TUE  |  WED  |  THU  |  FRI  |
+----+-------+-------+-------+-------+-------+
|  0 |  Bike |  Bike |  Walk |  Bike |  Car  |
|  1 |  Car  |  Car  |  Car  |  Bus  |  Car  |
|  2 |  Bus  | Train |  Bus  |  Bus  | Train |
|  3 |  Car  |  Car  |  Car  |  Walk |  Car  |
+----+-------+-------+-------+-------+-------+

我將如何分組並計算所有天數，以獲得每周運輸的總體模式。 例如：

+--------+-------+
|  MODE  | COUNT |
+--------+-------+
|  Bike  |   3   |
|   Bus  |   4   |
|   Car  |   9   |
|  Train |   2   |
|  Walk  |   2   |
+--------+-------+

我嘗試過使用：

SELECT COUNT(*), Mon 
FROM transport 
GROUP BY Mon, Tue, Wed, Thu, Fri

但是這會為每天的每個唯一值創建一個新組。

Answer 1

一種方法是生成一個子查詢，使用union all運算符在一列中選擇傳輸模式，然后計算出現次數：

SELECT   mode, COUNT(*)
FROM     (SELECT mon AS mode FROM transport UNION ALL
          SELECT tue AS mode FROM transport UNION ALL
          SELECT wed AS mode FROM transport UNION ALL
          SELECT thu AS mode FROM transport UNION ALL
          SELECT fri AS mode FROM transport) t
GROUP BY mode

Answer 2

如果您有一個單獨的模式表，您還可以：

select m.mode, count(*)
from modes m join
     transport t
     on m.mode in (t.mon, t.tue, t.wed, t.thu, t.fri)
group by m.mode;