选择特定列中重复值最多的行

Question

一般问题：我需要 select 一个 table 的值引用另一个 table.

中重复次数最多的值

表具有以下结构： screenshot screenshot2

问题是要找到与它相关的运动员结果最多的国家。

首先，INNER JOIN table在结果和国家/地区之间建立关系

SELECT competition_id, country FROM result
INNER JOIN sportsman USING (sportsman_id);

然后，我统计每个国家出现了多少次

SELECT country, COUNT(country) AS highest_participation
FROM (SELECT competition_id, country FROM result
    INNER JOIN sportsman USING (sportsman_id))
GROUP BY country
;

得到这个screenshot3

现在感觉我离解决方案只有一步之遥了)) 我猜还有一个 SELECT FROM (SELECT ...) 和 MAX() 是可能的，但我不能把它包起来？

ps: 我是通过像这样将查询加倍来做到这一点的，但我觉得如果有数百万行，它的效率就太低了。

SELECT country 
    FROM (SELECT country, COUNT(country) AS highest_participation
        FROM (SELECT competition_id, country FROM result 
            INNER JOIN sportsman USING (sportsman_id) 
            ) GROUP BY country 
        ) 
WHERE highest_participation = (SELECT MAX(highest_participation)  
    FROM (SELECT country, COUNT(country) AS highest_participation
        FROM (SELECT competition_id, country FROM result 
            INNER JOIN sportsman USING (sportsman_id) 
            ) GROUP BY country 
        ))

我也是用view做的

CREATE VIEW temp AS 
    SELECT country as country_with_most_participations, COUNT(country) as country_participate_in_#_comp 
    FROM( 
        SELECT country, competition_id FROM result 
        INNER JOIN sportsman USING(sportsman_id)
        ) 
    GROUP BY country;
SELECT country_with_most_participations FROM temp 
WHERE country_participate_in_#_comp = (SELECT MAX(country_participate_in_#_comp) FROM temp);

但不确定这是否是最简单的方法。

Answer 1

SELECT country 
    FROM (SELECT country, COUNT(country) AS highest_participation
        FROM (SELECT competition_id, country FROM result 
            INNER JOIN sportsman USING (sportsman_id) 
            ) GROUP BY country 
order by 2 desc
        ) 
where rownum=1

Answer 2

你似乎把这个复杂化了。从现有的 join 查询开始，您可以对结果进行聚合、排序并仅保留最上面的行。

select s.country, count(*) cnt
from sportsman s
inner join result r using (sportsman_id)
group by s.country
order by cnt desc
fetch first 1 row with ties

请注意，这允许顶部连接（如果有）。

Answer 3

如果我理解正确的话，您想要根据比赛次数对国家/地区进行排名，并显示排名最高的国家（或多个国家/地区）及其比赛次数。我建议你使用 RANK 进行排名。

select country, competition_count
from
(
  select 
    s.country,
    count(*) as competition_count,
    rank() over (order by count(*) desc) as rn
  from sportsman s
  inner join result r using (sportsman_id)
  group by s.country
) ranked_by_count
where rn = 1
order by country;

如果结果行的顺序无关紧要，您可以将其缩短为：

select s.country, count(*) as competition_count      
from sportsman s
inner join result r using (sportsman_id)
group by s.country
order by count(*) desc
fetch first rows with ties;

选择特定列中重复值最多的行

Selecting rows with the most repeated values at specific column

sql

oracle

inner-join

count

sql-order-by