1
+------------+---------+-------+-------------+--------+
| CampaignID | Medium | Month | Impressions | Clicks |
+------------+---------+-------+-------------+--------+
| A | Google | Jan | 15 | 2 |
| B | Google | Jan | 12 | 1 |
| A | YouTube | Jan | 11 | 2 |
| B | YouTube | Jan | 12 | 4 |
| A | Google | Feb | 15 | 3 |
| B | Google | Feb | 13 | 4 |
| A | YouTube | Feb | 12 | 2 |
| B | YouTube | Feb | 21 | 5 |
+------------+---------+-------+-------------+--------+
預期結果
+-----------+--------------------+---------------+---------------------+----------------+
| CampainID | Google Impressions | Google Clicks | YouTube Impressions | YouTube Clicks |
+-----------+--------------------+---------------+---------------------+----------------+
| A | 30 | 5 | 23 | 4 |
| B | 25 | 4 | 3 | 39 |
+-----------+--------------------+---------------+---------------------+----------------+
在運行時生成的值的在介質中需要的數量。這意味着查詢結果中的列數是動態依賴於數據。 PostgreSQL中最優雅的解決方案是什麼?
但我不知道有多少價值在那裏爲中等。明天我可以有另一個名爲「Facebook」的媒體,但我現在開發的解決方案必須足夠好才能滿足這種情況。即新的結果應該有2個額外的列。 –