連接兩個表，而只需要從外部表

Question

頂行我有兩個表：

表：series：

'id', 'series','thumbnail' 

表：videos：

'name','ref','sID' 

SID是的id的外鍵在表series中。我想要表series的前5行，第一個ref來自videos。

然而，我的SQL：

SELECT `series` , `thumbnail` , `ref` 
FROM `series` 
LEFT JOIN `videos` ON `videos`.`sID` = `series`.`id` 
ORDER BY `series`.`id` DESC 
LIMIT 0 , 5 

我最終從series第一頂行，但重複5次，用不同的裁判：

Youve Already Got It, image.jpg, fe4 
Youve Already Got It, image.jpg, 79c57 
Youve Already Got It, image.jpg, bd2 
Youve Already Got It, image.jpg, ff15c 
Youve Already Got It, image.jpg, 2ce 

Answer 1

試一下：

SELECT 
`series`, 
`thumbnail`, 
(SELECT `ref` FROM `videos` AS `v` WHERE `v`.`sID` = `s`.`id` LIMIT 0,1) AS `ref` 
FROM `series` AS `s` 
ORDER BY `series`.`id` DESC 
LIMIT 0,5 

Answer 2

假設你知道你在做什麼索引;）

SELECT *, (SELECT ref FROM videos WHERE sID = id LIMIT 1) as first_ref 
FROM series 
ORDER BY id 
LIMIT 5; 

Answer 3

你可以嘗試這樣也

SELECT `series` , `thumbnail` , `ref` 
FROM `series` 
INNER JOIN `videos` ON `videos`.`sID` = `series`.`id` 
GROUP BY `series`.`id` DESC 
LIMIT 0 , 5