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最新推荐文章于 2022-06-21 18:13:59 发布

原创最新推荐文章于 2022-06-21 18:13:59 发布 · 294 阅读

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本文介绍了一种使用SQL进行数据整理的方法，通过将学生姓名与各科成绩映射为键值对，实现数据的横向和纵向整合。此外还展示了如何利用CASE WHEN语句获取指定类别下的最高分。

--转成map，再取值

WITH student AS
(
SELECT '张三' AS name ,'语文' AS class, 100 AS score FROM system.dual UNION ALL
SELECT '张三' AS name ,'数学' AS class, 88 AS score FROM system.dual UNION ALL
SELECT '李四' AS name ,'语文' AS class, 98 AS score FROM system.dual UNION ALL
SELECT '李四' AS name ,'数学' AS class, 99 AS score FROM system.dual
)
WITH tb AS
(
SELECT
name,
str_to_map(CONCAT_WS(',',collect_list(concat(class,':',score))),',',':') as kv
FROM STUDENT GROUP BY name
)
SELECT name AS name,map_values(kv)[0] AS '语文',map_values(kv)[1] AS '数学' FROM tb;

--CASE WHEN 方式

WITH student AS
(
SELECT '张三' AS name ,'语文' AS class, 100 AS score FROM system.dual UNION ALL
SELECT '张三' AS name ,'数学' AS class, 88 AS score FROM system.dual UNION ALL
SELECT '李四' AS name ,'语文' AS class, 98 AS score FROM system.dual UNION ALL
SELECT '李四' AS name ,'语文' AS class, 99 AS score FROM system.dual
)
SELECT name AS name ,
max(CASE WHEN class='语文' THEN score ELSE NULL END ) AS '语文',
max(CASE WHEN class='数学' THEN score ELSE NULL END ) AS '数学'
FROM student
GROUP BY name;