这与 Limit results from joined table to one row 非常相似,但我正在努力让它完全按照我的需要工作......
表结构非常相似:
CREATE TABLE tblProducts (
intProductID int(11) NULL AUTO_INCREMENT,
strProductName varchar(255) NULL,
PRIMARY KEY (intProductID)
);
CREATE TABLE tblProductImages (
intImageID int(11) NULL AUTO_INCREMENT,
intProductID int(11) NULL,
strImageName varchar(255) NULL,
intOrder int(11) NULL,
PRIMARY KEY (intImageID)
);
用以下内容填充表格:
INSERT INTO tblProducts (strProductName)
VALUES
('Product #1'), ('Product #2'), ('Product #3');
INSERT INTO tblProductImages (intProductID, strImageName, intOrder)
VALUES
(1, 'image_for_1.jpg', 1),
(2, '1st_image_for_2.jpg', 1),
(2, '2nd_image_for_2.jpg', 2);
我想做一个返回所有 3 种产品的 SELECT,并带有适当的图像。类似于:
intProductID, strProductName, strImageName
1, Product #1, image_for_1.jpg
2, Product #2, 1st_image_for_2.jpg
3, Product #3, NULL
一个简单的解决方案是:
SELECT intProductID, strProductName,
(SELECT strImageName
FROM tblProductImages
WHERE tblProductImages.intProductID = tblProducts.intProductID
ORDER BY intOrder
LIMIT 1)
FROM tblProducts
但是如果我想从 tblProductImages 添加和返回另一个字段(例如 AltText),这会失败
我在 http://sqlfiddle.com/#!2/883c5/1 设置了一个 Fiddle
谢谢
最佳答案
这个可以用,但是很丑
select p.intProductId, p.strProductName, pi.strImageName
from tblProducts p
inner join tblProductImages pi on pi.intProductID = p.intProductId
inner JOIN (select min(intOrder) minOrder, intProductID
FROM tblProductImages
GROUP BY intProductID) s
on s.intProductID = p.intProductID and s.minOrder = pi.intOrder
union
select p.intProductId, p.strProductName, pi.strImageName
from tblProducts p
left join tblProductImages pi on pi.intProductID = p.intProductId
where pi.intProductID is null;
备选方案:
select p.intProductId, p.strProductName, pi.strImageName
from tblProducts p
left join tblProductImages pi on pi.intProductID = p.intProductId
where pi.intProductId is null or pi.IntOrder = (select min(intOrder)
from tblProductImages
where intProductId = pi.intProductId);
关于MySQL 为每个产品返回 1 张图像,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/20353403/