mySQL 左连接 5 个表？

Question

提前感谢您的帮助。我正在使用 mySQL 数据库中的 5 个表。该系统是这样的，我有一个名为“所有者”（客户）的顶级表，该表具有本地业务（商店）。这些所有者外出并在 yelp (citation_sources) 等网站上创建帐户，因此拥有登录凭据 (citation_login)。一旦他们在引文来源拥有帐户，他们就会将商店添加到目录中。

我希望创建一个查询来选择所有引文来源，无论所有者是否有帐户，并遍历记录集，同时显示他们拥有帐户的每个引文来源的登录信息与任何商店列表一样。

我的问题与在 5 个表上进行左连接有关。我遗漏了大部分字段，但设置了主键和外键连接的顺序是否重要，即。从一个特定的表开始，以另一个表结束？

我试过这个命令，但它只带回 33 行，而实际上有 96 个 citation_sources。

我想我明白了。我创建了一个名为“citation_shop”的新表，其中包含一个复合主键 - 引文 - 商店。然后我运行了一个查询，它得到了我想要的结果。我最终在第一个左连接中添加了一个条件。

SELECT citation_sources.name, citation_shop.shop from citation_sources left join citation_shop on citation_sources.id = citation_shop.citation 和 citation_shop.shop in (6,7) left join stores on citation_shop.shop = shop.id group by citation_sources.name , citation_shop.shop 限制 100

CREATE TABLE `citation_shop` (
  `shop` smallint(5) UNSIGNED NOT NULL,
  `citation` smallint(6) UNSIGNED NOT NULL,
  `url` text NOT NULL,
  `count` smallint(3) UNSIGNED NOT NULL,
  `status` tinyint(1) UNSIGNED NOT NULL,
  `sort` tinyint(3) UNSIGNED NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

--
-- Indexes for dumped tables
--

--
-- Indexes for table `citation_shop`
--
ALTER TABLE `citation_shop`
  ADD PRIMARY KEY (`citation`,`shop`);

select owners.id as owner_id, shops.id as shop_id, citation_sources.name, citation_shop_urls.url, citation_logins.password 
from owners 
inner join shops on owners.id = shops.owner_id 
left join citation_logins on owners.id = citation_logins.owner 
left join citation_sources on citation_logins.c_source = citation_sources.id 
left join citation_shop_urls on citation_sources.id = citation_shop_urls.citation_id 
where owners.id = 3 
group by citation_sources.name

这是我的表格，按我认为的相关性排序：

CREATE TABLE `owners` (
  `id` smallint(6) UNSIGNED NOT NULL,
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ;

CREATE TABLE `shops` (
  `id` smallint(5) UNSIGNED NOT NULL,
  `title` varchar(50) DEFAULT '',
  `owner_id` smallint(5) UNSIGNED NOT NULL,
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `citation_sources` (
  `id` smallint(6) UNSIGNED NOT NULL,
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `citation_shop_urls` (
  `shop` smallint(5) UNSIGNED NOT NULL DEFAULT '0',
  `citation_id` tinyint(5) UNSIGNED NOT NULL DEFAULT '0',
  `owner` smallint(6) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;


CREATE TABLE `citation_logins` (
  `c_source` smallint(5) UNSIGNED NOT NULL DEFAULT '0',
  `owner` smallint(6) NOT NULL,
  `user_name` text NOT NULL,
  `password` text NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

Answer 1

在LEFT JOIN 中，第一个表是您获取所有行的表，即使它们在其他表中没有匹配项。所以如果你想要所有citation_sources，即使是那些不与任何owner关联的，那么citation_sources应该是LEFT JOIN左边的表格。

要将所有者信息仅过滤到id = 3，请将o.id = 3 放在与owners 连接的ON 子句中。然后使用WHERE 子句删除所有其他行。

SELECT o.id as owner_id, s.id as shop_id, cs.name, u.url, cl.password 
FROM citation_sources AS cs
LEFT JOIN citation_shop_urls AS u ON u.citation_id = cs.id
LEFT JOIN citation_logins AS cl ON cs.id = cl.c_source
LEFT JOIN owners AS o ON o.id = cl.owner AND o.id = 3
LEFT JOIN shops AS s ON s.owner_id = o.id
WHERE o.id IS NULL OR o.id = 3