Question

我是学习SQL的新手，所以我提前道歉是我的问题是基本的。

我要做的是显示一个列，该列将分别告诉我在已经区分的＆＃34; old_country＆＃34;中已经分别具有百分比最高和最低值的国家/地区。和＆＃34; young_country＆＃34;：

SELECT
    CASE
        WHEN percent_aged_over_60 >= 10 THEN "old_country"
        WHEN percent_aged_over_60 < 10 THEN "young_country"
        ELSE "error"
    END AS "oldness",
COUNT(*)
FROM countries_by_population
    GROUP BY oldness;

换句话说，我想添加一个列，告诉我带有MAX（percent_aged_over_60）的国家名称＆＃34; old_country＆＃34;和＃34; young_country＆＃34;的MIN（percent_aged_over_60）。

虽然我确定这是最容易做的两个单独的查询，但我想在同一个查询中执行此操作。

因此，我正在寻找产生三列的结果 - 老，数（*）和国家。

Answer 1

使用此查询：

select t.country,t.oldness,count(*) from
(SELECT
 CASE
        WHEN percent_aged_over_60 >= 10 THEN "old_country"
        WHEN percent_aged_over_60 < 10 THEN "young_country"
        ELSE "error"
 END AS oldness
 , country
  ,*
 FROM countries_by_population) as t
 GROUP BY t.oldness,t.country;

Answer 2

使用子查询获取最小和最大百分比，然后将其与表格连接以获得与其匹配的国家/地区。

SELECT country,
        CASE
            WHEN percent_aged_over_60 >= 10 THEN "old_country"
            ELSE "young_country"
        END AS oldness,
        percent_aged_over_60
FROM countries_by_population
JOIN (SELECT MAX(percent_aged_over_60) AS max_pct, MIN(percent_aged_over_60) AS min_pct
      FROM countries_by_population) AS x
ON percent_aged_over_60 >= 10 AND percent_aged_over_60 = max_pct
    OR percent_aged_over_60 < 10 AND percent_aged_over_60 = min_pct

DEMO

选择具有MAX值的行，同时使用另一个GROUP BY

2 个答案: