如何在一个查询中从三个表中进行选择

Question

我有以下数据库结构：

db_config_list id | id_config | type

db_config id | id_list | name | value

db_config_lang id | id_list | id_lang | name |value

在一个 mySQL 查询中，我想从 db_config 和 db_config_lang 中选择内容，其中 db_config.id_list = db_config_list.id 和 db_config_lang.id_list = db_config_list.id

我试过了：

$sql = 'SELECT * FROM `'._DB_PREFIX_.$this->db_config_list.'` cl
        LEFT JOIN `'._DB_PREFIX_.$this->db_config.'` c
        ON (cl.id = c.id_list)
        LEFT JOIN `'._DB_PREFIX_.$this->db_config_lang.'` cll
        ON (cl.id = cll.id_list)
        WHERE cl.id_config = '.$this->c_id.'
        AND cl.type = "'.$this->c_type.'"
        AND cll.id_lang = "'.$this->default_lang.'"';

但它不能正常工作。当我在两个不同的查询中这样做时，它实际上是有效的：

$sql = 'SELECT * FROM `'._DB_PREFIX_.$this->db_config_list.'` cl
        LEFT JOIN `'._DB_PREFIX_.$this->db_config.'` c
        ON (cl.id = c.id_list)
        WHERE cl.id_config = '.$this->c_id.'
        AND cl.type = "'.$this->c_type.'"';

$sql = 'SELECT * FROM `'._DB_PREFIX_.$this->db_config_list.'` cl
        LEFT JOIN `'._DB_PREFIX_.$this->db_config_lang.'` cll
        ON (cl.id = cll.id_list)
        WHERE cll.id_lang = "'.$this->default_lang.'"';

但我想在一个查询中执行此操作。这可能吗？

// 编辑

我想我试图实现一些不可能的事情。所以我选择了不同的解决方案

$sql = 'SELECT name,value FROM `'._DB_PREFIX_.$this->db_config_list.'` cl
        LEFT JOIN `'._DB_PREFIX_.$this->db_config.'` c
        ON (cl.id = c.id_list)
        WHERE cl.id_config = '.$this->c_id.'
        AND cl.type = "'.$this->c_type.'"';

$sql2 = 'SELECT name,value FROM `'._DB_PREFIX_.$this->db_config_list.'` cl
        LEFT JOIN `'._DB_PREFIX_.$this->db_config_lang.'` cll
        ON (cl.id = cll.id_list)
        WHERE cll.id_lang = "'.$this->default_lang.'"';

$query1 =  Db::getInstance()->executeS($sql);
$query2 =  Db::getInstance()->executeS($sql2);

$query = array_merge($query1, $query2);

// 编辑 2

这是 sqlfiddle.com 的代码

创建代码：

CREATE TABLE IF NOT EXISTS `db_config_list` (
    `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
    `id_config` int(10) unsigned NOT NULL,
    `type` varchar(10) NOT NULL,
    PRIMARY KEY (`id`)
) DEFAULT CHARSET=UTF8;

CREATE TABLE IF NOT EXISTS `db_config` (
    `id_list` int(10) unsigned NOT NULL,
    `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
    `name` varchar(255) NOT NULL,
    `value` text NOT NULL,
    PRIMARY KEY (`id`)
) DEFAULT CHARSET=UTF8;


CREATE TABLE IF NOT EXISTS `db_config_lang` (
    `id_list` int(10) unsigned NOT NULL,
    `id_lang` int(10) unsigned NOT NULL,
    `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
    `name` varchar(255) NOT NULL,
    `value` text NOT NULL,
    PRIMARY KEY (`id`)
) DEFAULT CHARSET=UTF8;

ALTER TABLE `db_config` ADD INDEX(`id_list`);

ALTER TABLE `db_config_lang` ADD INDEX(`id_list`);

ALTER TABLE `db_config` ADD FOREIGN KEY (`id_list`) REFERENCES `db_config_list`(`id`) ON DELETE CASCADE ON UPDATE NO ACTION;

ALTER TABLE `db_config_lang` ADD FOREIGN KEY (`id_list`) REFERENCES `db_config_list`(`id`) ON DELETE CASCADE ON UPDATE NO ACTION;

INSERT INTO `db_config_list` (`id`, `id_config`, `type`) VALUES
(1, 1, 'global');

INSERT INTO `db_config` (`id_list`, `id`, `name`, `value`) VALUES
(1, 1, 'font_family', ''),
(1, 2, 'first_main_color', '#19BCE7'),
(1, 3, 'use_background_image', '1'),
(1, 4, 'background_color', '#F60'),
(1, 5, 'animated_tabs_carousel', '1'),
(1, 6, 'boxed_layout', '1'),
(1, 7, 'loading_animation', '1'),
(1, 8, 'smooth_scroll', '1'),
(1, 9, 'responsiveness', '1'),
(1, 10, 'sticky_header', '1');

INSERT INTO `db_config_lang` (`id_list`, `id_lang`, `id`, `name`, `value`) VALUES
(1, 1, 1, 'center_column_content', 'boo foo'),
(1, 1, 2, 'bottom_column_content', 'boo foo'),
(1, 2, 3, 'center_column_content', 'boo foo'),
(1, 2, 4, 'bottom_column_content', 'boo foo'),
(1, 3, 5, 'center_column_content', 'boo foo'),
(1, 3, 6, 'bottom_column_content', 'boo foo'),
(1, 4, 7, 'center_column_content', 'boo foo'),
(1, 4, 8, 'bottom_column_content', 'boo foo');

选择代码：

SELECT name,value FROM `db_config_list` cl
LEFT JOIN `db_config` c
ON (cl.id = c.id_list)
WHERE cl.id_config = 1
AND cl.type = "global";

SELECT name,value FROM `db_config_list` cl
LEFT JOIN `db_config_lang` cll
ON (cl.id = cll.id_list)
WHERE cll.id_lang = 1
AND cl.id_config = 1
AND cl.type = "global";

Answer 1

我认为正在发生的事情更有可能只是 select 是一个 * 属性 - 它只会为每个列名称选择一个值，而不管连接了多少表。如果您可以为此设置发布SQL Fiddle，我可以帮助您修改查询。从本质上讲，我相信您正在寻找类似的东西：

$sql = 'SELECT *, c.name AS config_name, cll.name as config_lang_name
        FROM `'._DB_PREFIX_.$this->db_config_list.'` cl
        LEFT JOIN `'._DB_PREFIX_.$this->db_config.'` c
        ON (cl.id = c.id_list)
        LEFT JOIN `'._DB_PREFIX_.$this->db_config_lang.'` cll
        ON (cl.id = cll.id_list)
        WHERE cl.id_config = '.$this->c_id.'
        AND cl.type = "'.$this->c_type.'"
        AND cll.id_lang = "'.$this->default_lang.'"';

编辑： 执行两个单独的查询然后合并结果集将比调整查询以返回所需的结果集要慢得多。这个查询更接近你想要的吗？ （以上只是一个例子，既然你已经展示了你的最终目标，我相信这应该可行。）

$sql = 'SELECT cl.name AS config_list_name, cl.value AS config_list_value,
        cll.name AS config_lang_name, cll.value AS config_lang_value
        FROM `'._DB_PREFIX_.$this->db_config_list.'` cl
        LEFT JOIN `'._DB_PREFIX_.$this->db_config.'` c
        ON (cl.id = c.id_list)
        LEFT JOIN `'._DB_PREFIX_.$this->db_config_lang.'` cll
        ON (cl.id = cll.id_list)
        WHERE cl.id_config = '.$this->c_id.'
        AND cl.type = "'.$this->c_type.'"
        AND cll.id_lang = "'.$this->default_lang.'"';

编辑 2： 看起来您正在为此查询使用框架。我真的建议使用一些参数绑定而不是将值直接放入查询中。