Question

总的来说，问题是：我需要从一个表中选择一个值，而该表要参考另一个表中重复最多的值。

问题是要找到与之相关的运动员成果最多的国家。

首先，INNER JOIN表将结果与国家/地区联系起来

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
;

并得到了这个screenshot3

现在感觉就像我离解决方案只有一步之遥）） 我想可以再使用SELECT FROM（SELECT ...）和MAX（），但我不能将其包装起来吗？

ps：我这样做是通过将查询加倍来实现的，但是如果有数百万行，我觉得效率很低。

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 
        ))

我也是有观点的

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

您似乎过于复杂了。从现有的join查询开始，您可以汇总，排序结果并仅保留第一行。

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，这可以保持最高的领带。

Answer 2

如果我正确理解这一点，则希望对每个比赛计数的国家/地区进行排名，并显示排名最高的一个或多个国家/地区。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，则可以将其缩短为：

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 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

选择特定列中重复值最高的行

3 个答案: