LeetCode（数据库）- 学生地理信息报告

Posted 2021-08-19 Lux_Sun

题目链接：点击打开链接

题目大意：略。

解题思路：原题此解决方案是需要一个前提——美洲学生最多，否则第 7 个用例通不过，如图所示，但题目没说，有点坑；进阶题是即使没有说明哪个洲学生最多也可以解（列转行思想）。

 

AC 代码

-- 原题
WITH t1 AS(SELECT *, ROW_NUMBER() OVER(ORDER BY name) rnk FROM student WHERE continent = 'America'),
t2 AS(SELECT *, ROW_NUMBER() OVER(ORDER BY name) rnk FROM student WHERE continent = 'Asia'),
t3 AS(SELECT *, ROW_NUMBER() OVER(ORDER BY name) rnk FROM student WHERE continent = 'Europe')

SELECT t1.name America, t2.name Asia, t3.name Europe
FROM t1 LEFT JOIN t2 ON t1.rnk = t2.rnk LEFT JOIN t3 ON t1.rnk = t3.rnk

-- 进阶
select
     max(case when continent='America' then name else null end) as America
    ,max(case when continent='Asia' then name else null end) as Asia
    ,max(case when continent='Europe' then name else null end) as Europe
from (SELECT *, row_number() over(partition by continent order by name) as rn from student) t
group by rn