將行轉換爲列 - 面臨的一個問題。

Question

我有以下數據集（請注意，我的數據庫/模式有點複雜，所以在這裏包含所有細節並不可行）

這是我從我的基表中提取的數據的簡化版本並創建了一個view。

 
workout_activity_record_id attribute_metric_id attribute_metric_value workout_exercise_set_created_on 
234        17    10       2012-02-06 00:00:00 
234        18    30       2012-02-06 00:00:00 
234        17    20       2012-03-03 00:00:00 
234        18    12.9      2012-03-03 00:00:00 
234        17    20       2012-04-02 00:00:00 
234        18    40       2012-04-02 00:00:00 
. 
. 
. (So on for further workout_activity_record_ids) 

我需要計算（查找數據，更好地瞭解）

Grand Total = (10 * 30) + (20 * 12.9) + (20 * 40)

按月分組。

這裏有助於乘法的基本方法是將行轉置爲列。因此，上述結構將成爲 -

 
workout_activity_record_id  ex17 ex18  workout_exercise_set_created_on  
234       10  30  2012-02-06 00:00:00 
234       20  12.9  2012-03-03 00:00:00 
234       20  40  2012-04-02 00:00:00 
. 
. 
. 
. 
. (And so on for remaining workout_activity_record_ids) 

對於這一點，我通過幾個竟然職位，嘗試了各種可行的/非後是活的（：d）選擇，我想出了下面的查詢。

 
SELECT 
     CASE attribute_metric_id 
      WHEN '17' THEN attribute_metric_value END AS 'ex17', 
     CASE attribute_metric_id WHEN '18' THEN attribute_metric_value END AS 'ex18', 
     workout_exercise_set_created_on 
FROM exercise_attribute 
WHERE workout_activity_record_id =234 

而且我得到的實際產量爲

 
workout_activity_record_id ex17 ex18 workout_exercise_set_created_on 
234       10  NULL 2012-02-06 00:00:00 
234       NULL 30  2012-02-06 00:00:00 
234       20  NULL 2012-03-03 00:00:00 
234       NULL 12.9 2012-03-03 00:00:00 
234       20  NULL 2012-04-06 00:00:00 
234       NULL 40  2012-04-02 00:00:00 

任何人都流下了這一些輕？我會很感激。謝謝！

Answer 1

此計算爲您共展宏圖，按年份和月份分組：

SELECT YEAR(workout_exercise_set_created_on) AS YEAR, 
     MONTH(workout_exercise_set_created_on) AS MONTH, 
     sum(SubTotal) AS GrandTotal 
FROM 
    (SELECT workout_exercise_set_created_on, 
      max(CASE WHEN attribute_metric_id = 17 THEN attribute_metric_value END) * max(CASE WHEN attribute_metric_id = 18 THEN attribute_metric_value END) AS SubTotal 
    FROM MyTable 
    GROUP BY workout_exercise_set_created_on) a 
GROUP BY YEAR(workout_exercise_set_created_on), 
     MONTH(workout_exercise_set_created_on) 

SQL Fiddle Example

輸出

YEAR MONTH GRANDTOTAL 
2012 2  300 
2012 3  258 
2012 4  800 

Answer 2

只需添加聚合函數：

SELECT 
    MAX(CASE attribute_metric_id 
     WHEN '17' THEN attribute_metric_value 
     END) AS 'ex17', 
    MAX(CASE attribute_metric_id 
     WHEN '18' THEN attribute_metric_value 
     END) AS 'ex18', 
    workout_exercise_set_created_on 
    FROM exercise_attribute 
    WHERE workout_activity_record_id =234 
    GROUP BY workout_exercise_set_created_on 

如果需要顯示不同workout_activity_record_id的結果，你應該修改group by workout_activity_record_id,workout_exercise_set_created_on