MySQL“情況”僅適用於某些價值

Question

我有下表：

id | date_inserted | type       | route_id | route_type | km
1    2016-01-05      Transport    null       Normal       null
2    2016-01-06      Transport    null       Normal       50
3    2016-01-07      Transport    1          Normal       null
4    2016-04-02      Transport    2          Normal       null
5    2016-05-03      Services     null       Normal       20
6    2016-06-21      Transport    null       Exceptional  35

我需要按月檢索總路線。 這是通過執行以下操作來完成的：

SELECT type, COUNT(id) AS `total`, MONTH(date_inserted) AS `month`
FROM routes
WHERE YEAR(date_inserted) = '2016' AND 
      type IN ('Transport', 'Services')
GROUP BY type, `month`
ORDER BY date_inserted ASC, `total` DESC

輸出類似於：

type       | total | month
Transport    3       1
Transport    1       2
Services     1       5
Transport    1       6

而且效果很好。 但是，現在要求我僅在類型為Transport時應用某些條件，這些條件如下：

1. route_id不能為null或
2. route_type必須為“ Exceptional或
3. route_type為“ Normal ”且km不等於零

因此，根據這種情況，這是我嘗試的方法：

SELECT type, COUNT(id) AS `total`, MONTH(date_inserted) AS `month`
FROM routes
WHERE YEAR(date_inserted) = '2016' AND 
      type IN ('Transport', 'Services') AND 
      (CASE WHEN type = 'Transport' THEN 
            route_id IS NOT NULL OR
            route_type = 'Exceptional' OR 
            (route_type = 'Normal' AND km != 0)
      END)
GROUP BY type, `month`
ORDER BY date_inserted ASC, `total` DESC

但是我的輸出是：

type       | total | month
Transport    2       1
Transport    1       2
Transport    1       6

Services行丟失。

Answer 1

您需要添加一個else段來處理服務。 如果希望是，則允許正常處理，請使用1 = 1。

SELECT type, COUNT(id) AS `total`, MONTH(date_inserted) AS `month`
FROM routes
WHERE YEAR(date_inserted) = '2016' AND 
  type IN ('Transport', 'Services') AND 
  (CASE WHEN type = 'Transport' THEN 
        route_id IS NOT NULL OR
        route_type = 'Exceptional' OR 
        (route_type = 'Normal' AND km != 0)
  ELSE 
  1 = 1
  END)
GROUP BY type, `month`
ORDER BY date_inserted ASC, `total` DESC

Answer 2

正如其他人所說，您需要在案例中添加一個ELSE ，否則當該行為“ Service”時，它將返回null且不顯示記錄。

SELECT type, COUNT(id) AS `total`, MONTH(date_inserted) AS `month`
FROM routes
WHERE YEAR(date_inserted) = '2016' AND 
      type IN ('Transport', 'Services') AND 
      (CASE WHEN type = 'Transport' THEN 
            route_id IS NOT NULL OR
            route_type = 'Exceptional' OR 
            (route_type = 'Normal' AND km != 0) 
            ELSE 1 = 1
      END)
GROUP BY type, `month`
ORDER BY date_inserted ASC, `total` DESC;

您可以使用的另一個版本（我更喜歡）是：

SELECT type, COUNT(id) AS `total`, MONTH(date_inserted) AS `month`
FROM routes
WHERE YEAR(date_inserted) = '2016' AND 
      (type = 'Services' OR 
            (type = 'Transport' and 
                    (route_id IS NOT NULL OR
                        route_type = 'Exceptional' OR 
                        (route_type = 'Normal' AND km != 0)
                    )
        )
      )
GROUP BY type, `month`
ORDER BY date_inserted ASC, `total` DESC;

如果route_type只能是“ Normal和“ Exceptional ，則可以更改條件：

SELECT type, COUNT(id) AS `total`, MONTH(date_inserted) AS `month`
FROM routes
WHERE YEAR(date_inserted) = '2016' AND 
      (type = 'Services' OR 
            (type = 'Transport' and 
                    (route_id IS NOT NULL OR
                     route_type = 'Exceptional' OR 
                     km != 0
                    )
        )
      )
GROUP BY type, `month`
ORDER BY date_inserted ASC, `total` DESC;