Mysql 如何连接表，同时限制第三个表中最近两行的数据？

我如何选择所有产品及其类别名称，以及每个产品只有两个最新价格

SELECT
    products.product_name,
    categories.category_name,
    prices.price
FROM
    products
INNER JOIN categories ON products.category_id = categories.id
INNER JOIN (
    SELECT
        prices.price,
    prices.product_id
    FROM
        prices
    ORDER BY
        created_at DESC
) as prices 
ON prices.product_id = products.id
GROUP BY products.product_name, categories.category_name, prices.price

产品

价格

类别

这是我的方法，它连接所有数据。若我在第二个内部联接上加上限制2，我总共只得到两行。如何获得所有产品，但每个产品只有两个最新价格

SELECT
    products.product_name,
    categories.category_name,
    prices.price
FROM
    products
INNER JOIN categories ON products.category_id = categories.id
INNER JOIN (
    SELECT
        prices.price,
    prices.product_id
    FROM
        prices
    ORDER BY
        created_at DESC
) as prices 
ON prices.product_id = products.id
GROUP BY products.product_name, categories.category_name, prices.price

这些数据可用于生成表和为表种子

SET FOREIGN_KEY_CHECKS=0;

DROP TABLE IF EXISTS `categories`;
CREATE TABLE `categories` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `category_name` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=4 DEFAULT CHARSET=latin1;

INSERT INTO `categories` VALUES ('1', 'fruits');
INSERT INTO `categories` VALUES ('2', 'vegetables');
INSERT INTO `categories` VALUES ('3', 'seeds');

DROP TABLE IF EXISTS `prices`;
CREATE TABLE `prices` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `price` int(11) DEFAULT NULL,
  `product_id` int(11) DEFAULT NULL,
  `created_at` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=17 DEFAULT CHARSET=latin1;

INSERT INTO `prices` VALUES ('1', '2', '1', '2017-01-07 04:03:45');
INSERT INTO `prices` VALUES ('2', '3', '2', '2017-01-07 04:03:45');
INSERT INTO `prices` VALUES ('3', '4', '3', '2017-01-07 04:03:45');
INSERT INTO `prices` VALUES ('4', '2', '4', '2017-01-07 04:03:45');
INSERT INTO `prices` VALUES ('5', '5', '1', '2017-02-07 04:03:45');
INSERT INTO `prices` VALUES ('6', '6', '2', '2017-02-07 04:03:45');
INSERT INTO `prices` VALUES ('7', '3', '3', '2017-02-07 04:03:45');
INSERT INTO `prices` VALUES ('8', '2', '4', '2017-02-07 04:03:45');
INSERT INTO `prices` VALUES ('9', '3', '1', '2017-03-10 06:03:45');
INSERT INTO `prices` VALUES ('10', '6', '2', '2017-03-10 06:03:45');
INSERT INTO `prices` VALUES ('11', '7', '3', '2017-03-10 06:03:45');
INSERT INTO `prices` VALUES ('12', '3', '4', '2017-03-10 06:03:45');
INSERT INTO `prices` VALUES ('13', '5', '1', '2017-03-10 09:03:45');
INSERT INTO `prices` VALUES ('14', '2', '2', '2017-03-10 09:03:45');
INSERT INTO `prices` VALUES ('15', '6', '3', '2017-03-10 09:03:45');

DROP TABLE IF EXISTS `products`;
CREATE TABLE `products` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `product_name` varchar(255) DEFAULT NULL,
  `category_id` int(11) NOT NULL,
  `created_at` date DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `f_category` (`category_id`)
) ENGINE=MyISAM AUTO_INCREMENT=5 DEFAULT CHARSET=latin1;

INSERT INTO `products` VALUES ('1', 'apples', '1', '2017-01-10');
INSERT INTO `products` VALUES ('2', 'pears', '1', '2017-01-10');
INSERT INTO `products` VALUES ('3', 'tomatoes', '2', '2017-01-10');
INSERT INTO `products` VALUES ('4', 'walnuts', '3', '2017-01-10');

---

您是否尝试过以下方法：

SELECT
    products.product_name,
    categories.category_name,
    prices.price
FROM
    products
INNER JOIN categories ON products.category_id = categories.id
INNER JOIN (
    SELECT TOP 2
        prices.price,
    prices.product_id
    FROM
        prices
    ORDER BY
        created_at DESC
) as prices 

试试这个。。使用价格限制表

SELECT products.product_name, categories.category_name, prices.price
FROM products
INNER JOIN categories ON products.category_id = categories.id
INNER JOIN (
SELECT prices.price, prices.product_id
FROM prices
ORDER BY created_at DESC 
LIMIT 2
) AS prices

---

注意：-西红柿是一种水果。

这不能正确连接，因此如果只有苹果的最新价格为5555，那么每种产品的价格都会相同。我使用MySQL，所以我想我不能使用SELECT TOP。但结果和@Muhammad写的一样

SELECT
    products.product_name,
    categories.category_name,
    prices.price
FROM
    products
INNER JOIN categories ON products.category_id = categories.id
INNER JOIN (
    SELECT TOP 2
        prices.price,
    prices.product_id
    FROM
        prices
    ORDER BY
        created_at DESC
) as prices 

SELECT products.product_name, categories.category_name, prices.price
FROM products
INNER JOIN categories ON products.category_id = categories.id
INNER JOIN (
SELECT prices.price, prices.product_id
FROM prices
ORDER BY created_at DESC 
LIMIT 2
) AS prices

SELECT products.product_name, categories.category_name, p.id,p.price
FROM products
INNER JOIN categories ON products.category_id = categories.id
INNER JOIN (
SELECT p.id,p.price, p.product_id,
         if(p.product_id <> @p, @rn:=1,@rn:=@rn+1) rn,
         @p:= p.product_id
FROM (select @rn:=0, @p:=0) rn,prices p
ORDER BY p.product_id, p.id DESC 
) AS p on p.product_id = products.id and (p.rn in (1,2))
order by products.id, p.id desc;