如何从三个表在一个查询中选择

Question

我有以下的数据库结构：

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的查询我想从db_config和db_config_lang其中db_config.id_list = db_config_list.id和db_config_lang.id_list = db_config_list.id

我试过选择的东西：

$sql = 'SELECT * FROM `'._DB_PREFIX_.$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.'"'; 

，但它不工作正确的。这是实际工作我做的时候这两个不同的查询：

$sql = 'SELECT * FROM `'._DB_PREFIX_.$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.'"'; 

但我想这样做在一个查询。这可能吗 ？

//编辑

我想我是想实现的东西是不可能的。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); 

// EDIT 2

这里是sqlfiddle.com

创建代码代码：

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

我在想，发生的事情更可能只是select是*属性 - 它将只为每个列名选择一个值，而不管有多少表连接。如果您可以发布此设置的SQL Fiddle，我可以帮助您修改查询。从本质上讲，我相信你正在寻找这样做：

$sql = 'SELECT *, c.name AS config_name, cll.name as config_lang_name 
     FROM `'._DB_PREFIX_.$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： 做两个单独的查询，然后合并结果集将远远超过调整查询返回所需的结果集慢。这个查询更接近你想要的吗？ （以上只是一个例子，现在你已经证明你的终极目标，我相信这应该工作。）

$sql = 'SELECT cl.name AS config_list_name, cl.value AS config_list_value, 
     cll.name AS config_lang_name, cll.value AS config_lang_value 
     FROM `'._DB_PREFIX_.$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： 看起来你正在使用这个查询的框架。我真的建议使用一些参数绑定，而不是直接将值放入查询中。