選擇不僅關係到另一個註冊表

Question

我模仿一個小型的數據庫更容易解釋最後插入的項目：

CREATE TABLE bands (
    id INTEGER UNSIGNED NOT NULL AUTO_INCREMENT, 
    name VARCHAR(120) NULL, 
    PRIMARY KEY(id) 
) 
TYPE=InnoDB; 

CREATE TABLE albums (
    id INTEGER UNSIGNED NOT NULL AUTO_INCREMENT, 
    band_id INTEGER UNSIGNED NOT NULL, 
    album_name VARCHAR(120) NULL, 
    rating INTEGER UNSIGNED NULL, 
    insertion_date TIMESTAMP NULL, 
    PRIMARY KEY(id), 
    INDEX albums_FKIndex1(band_id), 
    FOREIGN KEY(band_id) 
    REFERENCES bands(id) 
     ON DELETE NO ACTION 
     ON UPDATE NO ACTION 
) 
TYPE=InnoDB; 

現在，假裝我們已經有一些樂隊和他們各自的表中登記的多張唱片，我想僅選擇每個已註冊樂隊中最後插入的專輯。

PS：我必須使用「album.insertion_date」字段來確定哪個相冊是最後插入的。

Answer 1

嘗試通過insertion_date和帶連接兩個表和篩選：

SELECT al.* 
FROM albums al 
INNER JOIN bands b ON al.band_id=b.id 
WHERE al.insertion_date=(
    SELECT max(insertion_date) 
    FROM albums 
    WHERE band_id=b.id 
) 

Answer 2

試試這個：

select b.name, a.album_name, a.isertion_date 
    from bands b, albums a 
    where a.band_id = b.id 
    and a.insertion_date = (select max(a1.insertion_date) from albums a1 where a1.band_id = b.id) 

Answer 3

考慮到你的相冊IDS是AUTO_INCREMENT和可能性爲insertion_date是NULL（因爲它是默認值），使用insertion_date判定結果不這樣做，但最聰明的事...你去：

SELECT DISTINCT band, last_album, insertion_date 
FROM (
     SELECT bands.name AS band, albums.album_name AS last_album, albums.insertion_date 
     FROM bands 
     JOIN albums ON bands.id=albums.band_id 
     ORDER BY albums.insertion_date DESC 
    ) t1 
GROUP BY band;