MySQL 为每个产品返回 1 个图像 [英] MySQL returning 1 image for each product

问题描述

这与将连接表中的结果限制为一行非常相似，但我正在努力让它完全按照我的需要工作......

This is very similar to Limit results from joined table to one row, but I'm struggling to get it to work exactly as I need...

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)
);

使用以下内容填充表格:

Populate the tables with:

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 SELECT 返回所有 3 个产品，并带有适当的图像.类似于:

I want to do a SELECT that returns all 3 products, with appropriate images. Similar to:

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:

A simple solution would be:

SELECT intProductID, strProductName, 
 (SELECT strImageName
  FROM tblProductImages
  WHERE tblProductImages.intProductID = tblProducts.intProductID
  ORDER BY intOrder
  LIMIT 1)
FROM tblProducts

但是如果我想添加 &从 tblProductImages 返回另一个字段(例如 AltText)

But this fails if I want to add & return another field from the tblProductImages (AltText for example)

我在 http://sqlfiddle.com/#!2/设置了一个 Fiddle883c5/1

谢谢

推荐答案

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;

替代:

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);

Sqlfiddle

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