在一个查询中显示它所属的每个产品的所有类别

Question

如何在mysql中得到如下结果？

我想通过id获得所有产品组，并显示它属于哪个类别。
我怎样才能得到它在一个SQL？

SET FOREIGN_KEY_CHECKS=0; 

-- ---------------------------- 
-- Table structure for `a` 
-- ---------------------------- 
DROP TABLE IF EXISTS `a`; 
CREATE TABLE `a` (
    `products_id` int(11) NOT NULL, 
    `products_name` varchar(255) default NULL, 
    PRIMARY KEY (`products_id`) 
) ENGINE=MyISAM DEFAULT CHARSET=utf8; 

-- ---------------------------- 
-- Records of a 
-- ---------------------------- 
INSERT INTO `a` VALUES ('1', 'hello'); 
INSERT INTO `a` VALUES ('2', 'world'); 




SET FOREIGN_KEY_CHECKS=0; 

-- ---------------------------- 
-- Table structure for `b` 
-- ---------------------------- 
DROP TABLE IF EXISTS `b`; 
CREATE TABLE `b` (
    `products_id` int(11) NOT NULL, 
    `categories_id` int(11) NOT NULL, 
    PRIMARY KEY (`products_id`,`categories_id`) 
) ENGINE=MyISAM DEFAULT CHARSET=utf8; 

-- ---------------------------- 
-- Records of b 
-- ---------------------------- 
INSERT INTO `b` VALUES ('1', '1'); 
INSERT INTO `b` VALUES ('1', '2'); 
INSERT INTO `b` VALUES ('2', '1'); 
INSERT INTO `b` VALUES ('2', '3'); 

Answer 1

这是你想要的吗？

SELECT a.products_id, a.products_name, 
GROUP_CONCAT(CONVERT(b.categories_id,CHAR(8))) as products_to_categories 
FROM a,b 
WHERE a.products_id = b.products_id 
GROUP BY a.products_id, a.products_name 

小提琴在http://www.sqlfiddle.com/#!2/39edfc/3/0

在拨弄所得图像

Answer 2

存在由使用内的替代方式加入，欢呼=）

SELECT a.products_id, a.products_name,group_concat(b.categories_id) 
FROM a 
INNER JOIN b ON a.products_id = b.products_id 
group by a.products_id, a.products_name