按年度选择最小计数（'x'）

Posted 2023-02-01

我正在尝试创建一个表格，显示每年播放次数最少的歌曲。

例如，如果Song1和Song2都只有1次播放而Song3在2018年有2次播放而且Song1在2017年有1次播放而Song2在2017年有2次播放，我想要一个可以返回3行的表：

Song1 - 2018 - 1次播放

Song2 - 2018 - 1次播放

Song1 - 2017 - 1次发挥

有没有办法显示min（count（'x'））= count（'x'）的歌曲。我敢肯定这不是正确的语法，但它本质上是我想要找到的。

SELECT * FROM music 
NATURAL JOIN (SELECT extract(year from date) AS yr, song_code, COUNT('x') 
FROM singles NATURAL JOIN plays 
GROUP BY extract(year from date), song_code
ORDER BY yr desc, COUNT('x') desc);

目前我有按年份播放次数分组的歌曲，但我不确定如何只播放播放次数最少的歌曲。

答案

这应该工作。这也是为什么我们应该使用WITH（子查询因子分解）而不是内联视图的一个很好的例子。使用year，song_code和count创建一个song_count子查询。

另外，为了清楚起见，我会明确定义连接

WITH song_count as 
    SELECT extract(year from date) AS song_year, song_code, count(*) as play_count
    FROM singles NATURAL JOIN plays
    group by extract(year from date),song_code
select * from song_count
where
 (song_year,play_count) in (select song_year,min(play_count) from song_count group by song_year)

另一答案

- 您可以更喜欢使用分析函数，例如dense_rank()而不是连接或子查询。

with songs( id, year, play_id ) as
(
 select 1, 2018, 1 from dual union all    
 select 2, 2018, 1 from dual union all    
 select 3, 2018, 1 from dual union all
 select 3, 2018, 2 from dual union all
 select 1, 2017, 1 from dual union all 
 select 2, 2017, 1 from dual union all
 select 2, 2017, 2 from dual
)
select id, year, play_cnt
from
  (select s.*, dense_rank() over (partition by year order by play_cnt) dr
   from 
      (select id, year, count(play_id) as play_cnt
       from songs s
       group by id, year
      ) s
  )
where dr = 1;

        ID       YEAR   PLAY_CNT
---------- ---------- ----------
         1       2017          1
         2       2018          1
         1       2018          1

另一答案

你可以尝试使用row_number（）：

SELECT * 
FROM music 
NATURAL JOIN 
 (select yr, song_code, play_count
 from 
   (SELECT extract(year from date) AS yr, song_code, COUNT('x') play_count, row_number() over (partition by  extract(year from date), song_code order by COUNT('x')) rn
    FROM singles NATURAL JOIN plays 
    GROUP BY extract(year from date), song_code
   )
   where rn = 1;