Question

我有下面的查询工作正常，但它使用IN子句。有没有办法用JOIN替换IN子句？

SELECT p.*
FROM products as p
LEFT JOIN `product_categories` AS `pc` ON (`pc`.`product_id` = `p`.`product_id`)
WHERE pc.category_id IN (SELECT node.category_id 
FROM categories AS node, categories AS parent
WHERE node.left_node 
BETWEEN parent.left_node AND parent.right_node
AND parent.category_id = 6 ORDER BY node.left_node)

这里是我必须使用的表结构，它与IN子句一起正常工作，但我不知道，使用JOIN而不是IN子句获得相同的结果

--
-- Table structure for table `categories`
--

CREATE TABLE IF NOT EXISTS `categories` (
  `category_id` int(11) NOT NULL,
  `name` varchar(20) NOT NULL,
  `left_node` int(11) NOT NULL,
  `right_node` int(11) NOT NULL
) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=utf8;

--
-- Dumping data for table `categories`
--

INSERT INTO `categories` (`category_id`, `name`, `left_node`, `right_node`) VALUES
(1, 'electronics', 1, 20),
(2, 'televisions', 2, 9),
(3, 'tube', 3, 4),
(4, 'lcd', 5, 6),
(5, 'plasma', 7, 8),
(6, 'portable electronics', 10, 19),
(7, 'mp3 players', 11, 14),
(8, 'flash', 12, 13),
(9, 'cd players', 15, 16),
(10, '2 way radios', 17, 18);

-- --------------------------------------------------------

--
-- Table structure for table `products`
--

CREATE TABLE IF NOT EXISTS `products` (
  `product_id` int(11) NOT NULL,
  `name` varchar(40) DEFAULT NULL,
  `cat_id` int(11) NOT NULL
) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=utf8;

--
-- Dumping data for table `products`
--

INSERT INTO `products` (`product_id`, `name`, `cat_id`) VALUES
(1, '20" TV', 3),
(2, '36" TV', 3),
(3, 'Super-LCD 42"', 4),
(4, 'Ultra-Plasma 62"', 5),
(5, 'Value Plasma 38"', 5),
(6, 'Power-MP3 5gb', 7),
(7, 'Ipod 4gb', 8),
(8, 'Porta CD', 9),
(9, 'Walkman', 9),
(10, 'Family Talk 360', 10);

-- --------------------------------------------------------

--
-- Table structure for table `product_categories`
--

CREATE TABLE IF NOT EXISTS `product_categories` (
  `product_id` int(11) NOT NULL,
  `category_id` int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

--
-- Dumping data for table `product_categories`
--

INSERT INTO `product_categories` (`product_id`, `category_id`) VALUES
(1, 3),
(2, 3),
(3, 4),
(4, 5),
(5, 5),
(6, 7),
(7, 8),
(8, 9),
(9, 9),
(10, 10);

Answer 1

您需要JOIN node.category_id将其转换为

SELECT p.*
FROM products as p
LEFT JOIN `product_categories` AS `pc` ON `pc`.`product_id` = `p`.`product_id`
JOIN categories AS node ON pc.category_id = node.category_id
JOIN categories AS parent ON node.left_node BETWEEN parent.left_node AND parent.right_node
WHERE parent.category_id = 6
ORDER BY node.left_node;

如何使用JOIN而不是IN子句

1 个答案: