Write an SQL query to reformat the table such that there is a department id column and a revenue column for each month.
Return the result table in any order.
寫一個 SQL 查詢來重新格式化列表,像是每個月都有一個部門 id 和一個收入。 可任意排序結果。
Table: Department
+-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | revenue | int | | month | varchar | +-------------+---------+ (id, month) is the primary key of this table. The table has information about the revenue of each department per month. The month has values in ["Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"].
Example 1:
Input: Department table: +------+---------+-------+ | id | revenue | month | +------+---------+-------+ | 1 | 8000 | Jan | | 2 | 9000 | Jan | | 3 | 10000 | Feb | | 1 | 7000 | Feb | | 1 | 6000 | Mar | +------+---------+-------+ Output: +------+-------------+-------------+-------------+-----+-------------+ | id | Jan_Revenue | Feb_Revenue | Mar_Revenue | ... | Dec_Revenue | +------+-------------+-------------+-------------+-----+-------------+ | 1 | 8000 | 7000 | 6000 | ... | null | | 2 | 9000 | null | null | ... | null | | 3 | null | 10000 | null | ... | null | +------+-------------+-------------+-------------+-----+-------------+ Explanation: The revenue from Apr to Dec is null. Note that the result table has 13 columns (1 for the department id + 12 for the months).
Solution:
1. 選擇標題 id。
2. 將符合 month = [‘Jan’, ‘Feb’, ‘Mar’, ‘Apr’,
‘May’, ‘Jun’, ‘Jul’, ‘Aug’,
‘Sep’, ‘Oct’, ‘Nov’, ‘Dec’]
返回加總後的 revenue。
3. 來自 Department 的 table 。
4. 以 id 進行排序。
Code.1 CASE WHEN:
SELECT id, SUM(CASE WHEN (month = 'Jan') THEN revenue ELSE NULL END) AS Jan_Revenue, SUM(CASE WHEN (month = 'Feb') THEN revenue ELSE NULL END) AS Feb_Revenue, SUM(CASE WHEN (month = 'Mar') THEN revenue ELSE NULL END) AS Mar_Revenue, SUM(CASE WHEN (month = 'Apr') THEN revenue ELSE NULL END) AS Apr_Revenue, SUM(CASE WHEN (month = 'May') THEN revenue ELSE NULL END) AS May_Revenue, SUM(CASE WHEN (month = 'Jun') THEN revenue ELSE NULL END) AS Jun_Revenue, SUM(CASE WHEN (month = 'Jul') THEN revenue ELSE NULL END) AS Jul_Revenue, SUM(CASE WHEN (month = 'Aug') THEN revenue ELSE NULL END) AS Aug_Revenue, SUM(CASE WHEN (month = 'Sep') THEN revenue ELSE NULL END) AS Sep_Revenue, SUM(CASE WHEN (month = 'Oct') THEN revenue ELSE NULL END) AS Oct_Revenue, SUM(CASE WHEN (month = 'Nov') THEN revenue ELSE NULL END) AS Nov_Revenue, SUM(CASE WHEN (month = 'Dec') THEN revenue ELSE NULL END) AS Dec_Revenue FROM Department GROUP By id;
Code.2 IF:
SELECT id, SUM(IF(month = 'Jan', revenue, NULL)) AS Jan_Revenue, SUM(IF(month = 'Feb', revenue, NULL)) AS Feb_Revenue, SUM(IF(month = 'Mar', revenue, NULL)) AS Mar_Revenue, SUM(IF(month = 'Apr', revenue, NULL)) AS Apr_Revenue, SUM(IF(month = 'May', revenue, NULL)) AS May_Revenue, SUM(IF(month = 'Jun', revenue, NULL)) AS Jun_Revenue, SUM(IF(month = 'Jul', revenue, NULL)) AS Jul_Revenue, SUM(IF(month = 'Aug', revenue, NULL)) AS Aug_Revenue, SUM(IF(month = 'Sep', revenue, NULL)) AS Sep_Revenue, SUM(IF(month = 'Oct', revenue, NULL)) AS Oct_Revenue, SUM(IF(month = 'Nov', revenue, NULL)) AS Nov_Revenue, SUM(IF(month = 'Dec', revenue, NULL)) AS Dec_Revenue FROM Department GROUP By id;