选择特定列中重复值最多的行

Question

问题笼统地说：我需要从一个表中选择一个引用另一个表中重复次数最多的值的值。

表具有以下结构： screenshot screenshot2

问题是找到与它相关的运动员的成绩最多的国家。

首先，INNER JOIN 表在结果和国家/地区之间建立关系

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

然后，我计算每个国家出现的时间

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

得到了这个screenshot3

现在感觉我离解决方案只有一步之遥）） 我想可以再使用一个 SELECT FROM (SELECT ...) 和 MAX() 但我无法结束它？

ps： 我通过将这样的查询加倍来做到这一点，但如果有数百万行，我觉得效率太低了。

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 
        ))

我也是用视图来做的

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

如果我理解正确，您希望按比赛计数对国家/地区进行排名，并显示排名最高的国家（或多个国家）及其计数。我建议您使用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;

Answer 2

您似乎过于复杂了。从现有的 join 查询开始，您可以聚合、排序结果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，如果有的话，这允许顶级关系。

Answer 3

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