Question

以下行给出了错误消息。

$query = 'SELECT * FROM products AS p LEFT JOIN categories AS c USING ON c.id = p.category_id WHERE c.name = "Galleri1"
 AND p.status = "active"' ;
 $Q = $this->db->query($query);

数据库结构。类别

 CREATE TABLE IF NOT EXISTS `categories` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) NOT NULL,
  `shortdesc` varchar(255) NOT NULL,
  `longdesc` text NOT NULL,
  `status` enum('active','inactive') NOT NULL,
  `parentid` int(11) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=15 ;
...
...

产品

CREATE TABLE IF NOT EXISTS `products` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) NOT NULL,
  `shortdesc` varchar(255) NOT NULL,
  `longdesc` text NOT NULL,
  `thumbnail` varchar(255) NOT NULL,
  `image` varchar(255) NOT NULL,
  `class` varchar(255) DEFAULT NULL,
  `grouping` varchar(16) DEFAULT NULL,
  `status` enum('active','inactive') NOT NULL,
  `category_id` int(11) NOT NULL,
  `featured` enum('true','false') NOT NULL,
  `price` float(4,2) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=20 ;

错误消息

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ON c.id = p.category_id WHERE c.name = "Galleri1" AND p.status = "active"' at line 1

SELECT * FROM products AS p LEFT JOIN categories AS c USING ON c.id = p.category_id WHERE c.name = "Galleri1" AND p.status = "active"

Q1。任何人都可以指出我的错误吗？

Q2。谁能告诉我如何在Codeigniter的Active Record课程中写这个？

提前致谢。

Answer 1

使用单引号，摆脱USING并使JOIN内部：

SELECT  *
FROM    products AS p
JOIN    categories AS c
ON      c.id = p.category_id
WHERE   c.name = 'Galleri1'
        AND p.status = 'active'

双引号用于标记用作表名和列名的保留字。字符串文字应括在单引号中。
JOIN USING (col1)表示您在两个表中都有一个名为col1的字段，并希望加入该字段。如果不这样做，则应使用JOIN ON
将此条件c.name = 'Galleri1'置于WHERE子句中会使LEFT JOIN返回与INNER JOIN完全相同的记录。后者更有效（因为优化器可以选择在连接中引导哪个表）。

Answer 2

USING和ON是两种不同的方式来确定与哪些列进行连接。您的查询指定了两者，但看起来您尝试使用ON语法。请尝试以下方法：

SELECT * FROM products AS p LEFT JOIN categories AS c ON c.id = p.category_id WHERE c.name = "Galleri1"

mySQL加入问题

2 个答案: