从 3 个不同的表中选择项目

Question

我想从3个不同的表中选择项目，我使用UNION，但是列数不同，所以它返回列数错误，有没有其他方法使用JOIN来获得赞赏结果？

SELECT * 
FROM `ads` JOIN ad_car 
      ON ads.id_ads = ad_car.main_ad 
WHERE ads_cat = :ads_cat AND 
      ads.ad_status = :adStatus 
UNION 
SELECT * 
FROM `ads` JOIN ad_vehpro 
      ON ads.id_ads = ad_vehpro.main_ad 
WHERE ads_cat = :ads_cat AND 
      ads.ad_status = :adStatus 
ORDER BY date_renewed 
DESC LIMIT 4

已编辑：我添加了表格：

CREATE TABLE IF NOT EXISTS `ads` (
  `id_ads` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `id_profiles_key` varchar(20) NOT NULL,
  `id_shops` int(4) NOT NULL DEFAULT '1',
  `ads_cat` int(2) NOT NULL COMMENT 'main category: vehicule, immobilier,...',
  `ads_scat` int(3) NOT NULL COMMENT 'sous cat: voiture, moto,...',
  `form_id` varchar(30) NOT NULL COMMENT 'form key',
  `city_id` int(5) NOT NULL,
  `district_id` int(5) NOT NULL,
  `adtype_id` int(1) NOT NULL DEFAULT '1' COMMENT '1: offre, 2: demande',
  `ads_title` varchar(200) NOT NULL,
  `ads_description` longtext NOT NULL,
  `ads_price` int(11) NOT NULL,
  `num_img` int(2) NOT NULL DEFAULT '1' COMMENT 'number of images',
  `num_vid` int(2) NOT NULL DEFAULT '0' COMMENT 'number of video',
  `num_com` int(3) NOT NULL DEFAULT '0' COMMENT 'number of comments',
  `to_pin` int(1) NOT NULL DEFAULT '0' COMMENT 'ad that will be pinned. 0: no, 1: yes',
  `date_inserted` varchar(20) NOT NULL,
  `date_modified` varchar(20) NOT NULL,
  `date_renewed` varchar(20) NOT NULL,
  `date_pinned` varchar(20) NOT NULL DEFAULT '0',
  `ad_status` int(1) NOT NULL DEFAULT '1' COMMENT '0: not active, 1: active, 2: deleted, 3: pinned',
  PRIMARY KEY (`id_ads`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=7 ;


    CREATE TABLE IF NOT EXISTS `ad_car` (
  `id_ad` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `main_ad` int(5) NOT NULL COMMENT 'this will refer to main table ads (id_ads)',
  `id_profiles` varchar(20) NOT NULL,
  `city_id` int(5) NOT NULL,
  `district_id` int(5) NOT NULL COMMENT 'district id from districts table',
  `category_id` int(2) NOT NULL,
  `make_id` int(5) NOT NULL,
  `model_id` int(5) NOT NULL,
  `model_year` int(4) NOT NULL,
  `engine` int(2) NOT NULL,
  `fuel` int(1) NOT NULL,
  `mileage` bigint(7) NOT NULL,
  `transmission` int(1) NOT NULL,
  `wheed_drive` int(1) NOT NULL,
  `in_color` varchar(7) NOT NULL,
  `ex_color` varchar(7) NOT NULL,
  `seats` int(2) NOT NULL,
  `doors` int(1) NOT NULL,
  `tax` varchar(5) NOT NULL,
  `warranty` int(1) NOT NULL,
  `hands` int(1) NOT NULL,
  `security` longtext NOT NULL,
  `comfort` longtext NOT NULL,
  `aesthetic` longtext NOT NULL,
  `adreference` varchar(10) NOT NULL,
  `ad_price` bigint(20) NOT NULL,
  `ad_priceneg` int(1) NOT NULL,
  `when_inserted` varchar(20) NOT NULL,
  `when_modified` varchar(20) NOT NULL,
  `ad_status` int(1) NOT NULL DEFAULT '1' COMMENT '0: not active, 1: active, 2: deleted',
  `not_listed` longtext NOT NULL,
  PRIMARY KEY (`id_ad`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=6 ;


    CREATE TABLE IF NOT EXISTS `ad_vehpro` (
  `id_ad` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `main_ad` int(5) NOT NULL COMMENT 'this will refer to main table ads (id_ads)',
  `id_profiles` varchar(20) NOT NULL,
  `city_id` int(5) NOT NULL,
  `district_id` int(5) NOT NULL COMMENT 'district id from districts table',
  `category_id` int(2) NOT NULL,
  `vehpro_type` int(1) NOT NULL,
  `make_id` int(5) NOT NULL,
  `model_id` int(5) NOT NULL,
  `model_year` int(4) NOT NULL,
  `engine` int(2) NOT NULL,
  `fuel` int(1) NOT NULL,
  `mileage` bigint(7) NOT NULL,
  `transmission` int(1) NOT NULL,
  `wheed_drive` int(1) NOT NULL,
  `in_color` varchar(7) NOT NULL,
  `ex_color` varchar(7) NOT NULL,
  `seats` int(2) NOT NULL,
  `doors` int(1) NOT NULL,
  `tax` varchar(5) NOT NULL,
  `warranty` int(1) NOT NULL,
  `hands` int(1) NOT NULL,
  `security` longtext NOT NULL,
  `comfort` longtext NOT NULL,
  `aesthetic` longtext NOT NULL,
  `adreference` varchar(10) NOT NULL,
  `ad_price` bigint(20) NOT NULL,
  `ad_priceneg` int(1) NOT NULL,
  `when_inserted` varchar(20) NOT NULL,
  `when_modified` varchar(20) NOT NULL,
  `ad_status` int(1) NOT NULL DEFAULT '1' COMMENT '0: not active, 1: active, 2: deleted',
  `not_listed` longtext NOT NULL,
  PRIMARY KEY (`id_ad`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=2 ;

已编辑

我尝试使用 LEFT JOIN，但它跳过了一些字段：

$sqlAds = "SELECT * FROM `ads`"
                . " LEFT JOIN ad_car ON ads.id_ads = ad_car.main_ad"
                . " LEFT JOIN ad_vehpro ON ads.id_ads = ad_vehpro.main_ad"
                . " WHERE ads_cat = :ads_cat AND ads.ad_status = :adStatus ORDER BY date_renewed DESC";

提前致谢

Answer 1

列出您明确想要的列。为其余部分提供NULLvalues：

SELECT a.*, c.col1, c.col2
FROM `ads` a JOIN
      ad_car c
      ON a.id_ads = c.main_ad 
WHERE ads_cat = :ads_cat AND 
      a.ad_status = :adStatus 
UNION 
SELECT a.*, v.col1, NULL as col2
FROM ads a JOIN
     ad_vehpro v
     ON a.id_ads = v.main_ad 
WHERE ads_cat = :ads_cat AND 
      a.ad_status = :adStatus 
ORDER BY date_renewed DESC
LIMIT 4;

注意：如果您知道两个子查询之间没有重复，请使用UNION ALL 而不是UNION。 UNION 会产生删除重复项的开销。