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题目：（简单）
| 解法 | 执行用时 |
|---|---|
| Ans 1 (Python) | 409ms (38.77%) |
| Ans 2 (Python) | 489ms (16.33%) |
| Ans 3 (Python) | 422ms (33.30%) |
LeetCode的Python执行用时随缘，只要时间复杂度没有明显差异，执行用时一般都在同一个量级，仅作参考意义。
解法一：
SELECT id, SUM(CASE `month` WHEN 'Jan' THEN revenue END) Jan_Revenue, SUM(CASE `month` WHEN 'Feb' THEN revenue END) Feb_Revenue, SUM(CASE `month` WHEN 'Mar' THEN revenue END) Mar_Revenue, SUM(CASE `month` WHEN 'Apr' THEN revenue END) Apr_Revenue, SUM(CASE `month` WHEN 'May' THEN revenue END) May_Revenue, SUM(CASE `month` WHEN 'Jun' THEN revenue END) Jun_Revenue, SUM(CASE `month` WHEN 'Jul' THEN revenue END) Jul_Revenue, SUM(CASE `month` WHEN 'Aug' THEN revenue END) Aug_Revenue, SUM(CASE `month` WHEN 'Sep' THEN revenue END) Sep_Revenue, SUM(CASE `month` WHEN 'Oct' THEN revenue END) Oct_Revenue, SUM(CASE `month` WHEN 'Nov' THEN revenue END) Nov_Revenue, SUM(CASE `month` WHEN 'Dec' THEN revenue END) Dec_RevenueFROM DepartmentGROUP BY id;
解法二：
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 Departmentgroup by id;
解法三：
select id, max(case when month = 'Jan' then revenue end) Jan_Revenue, max(case when month = 'Feb' then revenue end) Feb_Revenue, max(case when month = 'Mar' then revenue end) Mar_Revenue, max(case when month = 'Apr' then revenue end) Apr_Revenue, max(case when month = 'May' then revenue end) May_Revenue, max(case when month = 'Jun' then revenue end) Jun_Revenue, max(case when month = 'Jul' then revenue end) Jul_Revenue, max(case when month = 'Aug' then revenue end) Aug_Revenue, max(case when month = 'Sep' then revenue end) Sep_Revenue, max(case when month = 'Oct' then revenue end) Oct_Revenue, max(case when month = 'Nov' then revenue end) Nov_Revenue, max(case when month = 'Dec' then revenue end) Dec_Revenuefrom Departmentgroup by id;
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