MySQL左联接（未知列）

Question

我的查询有问题。

MySQL查询：

SELECT DISTINCT(`users`.`username`), `users`.`full_name`, `users`.`profile_picture_url`, 
`users`.`followed_by_count`, `users`.`follows_count`, `users`.`bio`, `users`.`id`
FROM `users`,`interests`
LEFT JOIN `blocked` 
ON `blocked`.`receiver_id` = `users`.`id`
AND `blocked`.`actor_id` = 100 
AND `blocked`.`blocked_reason` = 'Blocked'
WHERE `blocked`.`receiver_id` IS NULL 
AND `users`.`instagram_active` = 1 
AND `users`.`banned` = 0 
AND `interests`.`user_id` = `users`.`id` 
AND `interests`.`interest` = 'Food'
AND `interests`.`active` = 1 
AND `users`.`active` = 1
ORDER BY `users`.`last_login` DESC
LIMIT 0, 25

我得到的错误是这样的：

选择时如何将其作为未知列？

我很困扰…

使用者：

CREATE TABLE `users` (    
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
 `instagram_id` int(11) NOT NULL,
 `username` varchar(100) COLLATE utf8_unicode_ci NOT NULL,
 `bio` text COLLATE utf8_unicode_ci,
 `website` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
 `profile_picture_url` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
 `full_name` varchar(200) COLLATE utf8_unicode_ci NOT NULL,
 `media_count` int(11) unsigned NOT NULL,
 `followed_by_count` int(11) unsigned NOT NULL,
 `follows_count` int(11) unsigned NOT NULL,
 `last_updated` datetime NOT NULL,
 `last_updated_instagram` datetime NOT NULL,
 `instagram_active` tinyint(1) DEFAULT NULL,
 `last_login` datetime NOT NULL,
 `inserted_on` datetime NOT NULL,
 `banned` tinyint(1) NOT NULL DEFAULT '0',
 `banned_reason` text COLLATE utf8_unicode_ci,
 `oauth_token` varchar(150) COLLATE utf8_unicode_ci NOT NULL,
 `user_level` tinyint(4) NOT NULL,
 `shown_to_others` tinyint(1) NOT NULL DEFAULT '1',
 `credits_offered` tinyint(1) unsigned NOT NULL DEFAULT '2',
 `active` tinyint(1) NOT NULL DEFAULT '1',
 `email` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
 `registered_ip` varchar(17) COLLATE utf8_unicode_ci DEFAULT NULL,
 `credits` int(11) NOT NULL,
 `email_notifications` tinyint(1) NOT NULL DEFAULT '1',
 `todays_followers` int(11) NOT NULL DEFAULT '0',
 `todays_followers_hour` int(11) NOT NULL,
 `total_followers` int(11) NOT NULL,
 `credits_yesterday` int(11) NOT NULL,
 `email_is_verified` tinyint(1) NOT NULL DEFAULT '0',
 `email_announcements` tinyint(1) NOT NULL DEFAULT '1',
 `email_credits` tinyint(1) NOT NULL DEFAULT '1',
 `verification_code` varchar(25) COLLATE utf8_unicode_ci DEFAULT NULL,
 `country_id` bigint(20) unsigned DEFAULT NULL,
 `browser_info_id` bigint(20) unsigned DEFAULT NULL,
 `featured_user` tinyint(1) NOT NULL DEFAULT '0',
 `emailed_credits` tinyint(1) NOT NULL DEFAULT '0',
 UNIQUE KEY `id` (`id`),
 UNIQUE KEY `instagram_id` (`instagram_id`),
 KEY `country_id` (`country_id`),
 KEY `browser_info_id` (`browser_info_id`),
 KEY `username` (`username`,`instagram_active`,`banned`),
 CONSTRAINT `users_ibfk_1` FOREIGN KEY (`country_id`) REFERENCES `countries` (`id`) ON DELETE SET NULL ON UPDATE CASCADE,
 CONSTRAINT `users_ibfk_2` FOREIGN KEY (`browser_info_id`) REFERENCES `browser_info` (`id`) ON DELETE SET NULL ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=1279 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

兴趣：

CREATE TABLE `interests` (
 `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
 `user_id` bigint(20) unsigned NOT NULL,
 `interest` varchar(25) COLLATE utf8_unicode_ci NOT NULL,
 `inserted_dt` datetime NOT NULL,
 `active` tinyint(1) NOT NULL DEFAULT '1',
 UNIQUE KEY `id` (`id`),
 KEY `user_id` (`user_id`),
 KEY `interest` (`interest`),
 CONSTRAINT `interests_ibfk_1` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=4161 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

已封锁：

CREATE TABLE `blocked` (
 `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
 `actor_id` bigint(20) unsigned NOT NULL,
 `receiver_id` bigint(20) unsigned DEFAULT NULL,
 `blocked_reason` enum('Skipped','Blocked') COLLATE utf8_unicode_ci NOT NULL,
 `inserted_dt` datetime NOT NULL,
 `active` tinyint(1) NOT NULL DEFAULT '1',
 `browser_info_id` bigint(20) unsigned DEFAULT NULL,
 UNIQUE KEY `id` (`id`),
 KEY `actor_id` (`actor_id`,`receiver_id`),
 KEY `receiver_id` (`receiver_id`),
 KEY `browser_info_id` (`browser_info_id`),
 CONSTRAINT `blocked_ibfk_1` FOREIGN KEY (`actor_id`) REFERENCES `users` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
 CONSTRAINT `blocked_ibfk_2` FOREIGN KEY (`receiver_id`) REFERENCES `users` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
 CONSTRAINT `blocked_ibfk_3` FOREIGN KEY (`browser_info_id`) REFERENCES `browser_info` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=5700 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

Answer 1

如JOIN语法所示：

在MySQL 5.0.12中加入处理更改

[ deletia ]

• 以前，逗号运算符（,）和JOIN都具有相同的优先级，因此join表达式t1, t2 JOIN t3被解释为((t1, t2) JOIN t3)。现在JOIN具有更高的优先级，因此该表达式被解释为(t1, (t2 JOIN t3))。此更改会影响使用ON子句的语句，因为该子句只能引用联接操作数中的列，并且优先级的更改会更改对这些操作数的解释。

例子：

>     创建表t1（i1 INT，j1 INT）;
创建表t2（i2 INT，j2 INT）;
创建表t3（i3 INT，j3 INT）;
插入t1值（1,1）;
插入t2值（1,1）;
插入t3值（1,1）;
选择* FROM t1，t2 JOIN t3 ON（t1.i1 = t3.i3）;

以前，SELECT由于t1,t2as的隐式分组，所以合法(t1,t2)。现在JOIN优先，所以ON子句的操作数是t2和t3。因为t1.i1这两个操作数都不是列，所以结果是Unknown column 't1.i1' in 'on clause'错误。要允许处理连接，请使用括号将前两个表显式分组，以便该ON子句的操作数为(t1,t2)和t3：

>     选择* FROM（t1，t2）JOIN t3 ON（t1.i1 = t3.i3）;

另外，请避免使用逗号运算符，而应使用JOIN：

>     选择* FROM t1 JOIN t2 JOIN t3 ON（t1.i1 = t3.i3）;

这种变化也适用于与混合逗号操作语句INNER JOIN，CROSS JOIN，LEFT JOIN，并且RIGHT JOIN，所有这些现在已经比逗号运算符优先级越高。