在 Postgres SQL 中将列值更改为列标题，替换为另一列中的值

Question

我无法弄清楚如何将列值制作为列标题并在发生时分配适当的值

假设我有一个带有下表的 Postgres 数据库：

 Name      Subject       Score      Region
=======   =========     =======     =======
 Joe       Chemistry      20        America 
 Robert    Math           30        Europe
 Jason     Physics        50        Europe
 Joe       Math           70        America
 Robert    Physics        80        Europe
 Jason     Math           40        Europe
 Jason     Chemistry      60        Europe

我想以以下形式选择/获取数据：

 Name      Chemistry     Math       Physics     Region
=======   ==========    =======    ========    ========
 Joe        20            70         null       America
 Robert     null          30         80         Europe
 Jason      60            40         50         Europe
 

考虑到有80个科目。 如何编写以这种格式返回数据的 SQL 选择语句？

Answer 1

如果主题列表仅限于您在示例中提到的 3 个，则查询可能看起来像链接以下内容：

SELECT
    name,
    MAX(CASE WHEN subject LIKE 'Chemistry' THEN score END) AS "Chemistry",
    MAX(CASE WHEN subject LIKE 'Math' THEN score END) AS "Math",
    MAX(CASE WHEN subject LIKE 'Physics' THEN score END) AS "Physics"

FROM grades
GROUP BY name

Answer 2

在 Postgres 中，我建议使用FILTER语法进行条件聚合：

SELECT name,
       MAX(score) FILTER (WHERE subject = 'Chemistry') AS Chemistry,
       MAX(score) FILTER (WHERE subject = 'Math') AS Math,
       MAX(score) FILTER (WHERE subject = 'Physics') AS Physics
FROM grades
GROUP BY name