SQL窗口函數 - 按限制選擇DISTINCT ORDER

Question

我在PostgreSQL數據庫中有這3個表：

• 藝術家： id，名字
• 專輯： id，title，year，artist_id
• 歌曲： id，title，album_id

基本上每個藝術家都有多個專輯，每個專輯都有多首歌曲。

我的查詢正確地返回了25個不同的artist.id，其中一首歌的標題以“The”開頭，以相冊的年份排序：

SELECT id
FROM (

    -- Remove the duplicate artists
    SELECT DISTINCT ON (a.id) id, row
    FROM (

        -- Get all matching artists 
        -- This is slow because there is no limit
        SELECT
            artist.id,
            row_number() OVER(ORDER BY album.year DESC) as row
        FROM artist
        LEFT JOIN album ON album.artist_id = artist.id
        LEFT JOIN song ON song.album_id = album.id
        WHERE song.title ilike 'The %'
        ORDER BY album.year DESC

    ) as a

) as b
ORDER BY row
LIMIT 25

然而，它是緩慢且低效的，因為最里面的查詢沒有LIMIT，所以它將在整個表中搜索所有可能的匹配。 理想情況下，當找到25個不同的artist.id時，它會停止搜索。

可以重寫或優化此查詢以更快地執行嗎？

我認為窗口函數可以加速這里的事情，但我無法找出有用的東西。

謝謝！

Answer 1

select id, year
from (
    SELECT DISTINCT ON (artist.id) artist.id, album.year
    FROM artist
    inner JOIN album ON album.artist_id = artist.id
    inner JOIN song ON song.album_id = album.id
    WHERE song.title ilike 'The %'
    ORDER BY artist.id, album.year DESC
) s
order by year desc
LIMIT 25

當ilike表達式以%開頭時， song.title上的索引可以提供幫助

Answer 2

試試這個，應該比你當前的查詢更快

SELECT
  artist.id,                        
  MAX( album.year ) as latest_album_date
FROM 
  artist
  JOIN album ON album.artist_id = artist.id  -- JOIN, not LEFT JOIN
  JOIN song ON song.album_id = album.id      -- Since you have song.title in WHERE clause, it makes no sense to make these as a LEFT JOIN
WHERE 
  song.title ilike 'The %'
GROUP BY
  artist.id
ORDER BY
  latest_album_date DESC
limit 25;

SQLFIDDLE

Answer 3

試試這個，

Select id, year
from (
    SELECT DISTINCT ON (artist.id) artist.id, album.year
    FROM artist
    rightJOIN album ON album.artist_id = artist.id
    left JOIN song ON song.album_id = album.id
    WHERE song.title ilike 'The %'
    ORDER BY artist.id, album.year DESC
) s
order by year desc
LIMIT 25