通過

Question

訂購後選擇一條記錄我有一堆CD包含一堆藝術品。我想在網頁上顯示每張CD的拇指圖像，爲此，我需要從CD中存在的許多作品中挑選一張圖像...

查詢選擇所有藝術作品和我的組按位置，並希望選擇第一個。我不就沒怎麼只選擇第一個圖像的每個記錄後，我命令他們......

查詢是如下：

SELECT release_artwork.release_id, release_artwork.position, artwork.small_filename, artwork.small_width, artwork.small_height 
FROM release_artwork 
JOIN artwork ON artwork.artwork_id = release_artwork.artwork_id 
ORDER BY release_artwork.position 

Answer 1

我沒有方便的MySQL實例，但這應該工作 - 只需定義一個內聯表來保存最小值，然後加入到那個。

SELECT release_artwork.release_id, release_artwork.position, artwork.small_filename, artwork.small_width, artwork.small_height 
FROM 
    release_artwork 
    inner JOIN artwork ON artwork.artwork_id = release_artwork.artwork_id 
    inner join 
    (
    SELECT 
    ra.release_id as release_id 
    ,min(ra.position) as rap 
    FROM 
    release_artwork ra 
    group by 
    ra.release_id 
) mins 
    on mins.release_id = release_artwork.release_id 
    and mins.rap = release_artwork.position 
ORDER BY 
    release_artwork.release_id 

Answer 2

在這種情況下，你可以使用LIMIT 1，將您檢索的結果限制爲僅第一個。

Answer 3

SELECT release_artwork.release_id, release_artwork.position, artwork.small_filename, artwork.small_width, artwork.small_height 
FROM release_artwork 
JOIN artwork ON artwork.artwork_id = release_artwork.artwork_id 
ORDER BY release_artwork.position LIMIT 1 

在末端添加LIMIT 1將其限定爲單個結果。