MySQL左联接(未知列) [英] MySQL Left Join (Unknown Column)

问题描述

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:

1054-"on子句"中的未知列"users.id"

当我选择它时，它如何为未知列?

How is it an unknown column when I am SELECTing it?

我很困惑...

用户:

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

推荐答案

如 JOIN语法所述a>:

As documented under JOIN Syntax:

MySQL 5.0.12中的联接处理更改

[ deletia ]

• 以前，逗号运算符(,)和JOIN都具有相同的优先级，因此联接表达式t1, t2 JOIN t3被解释为((t1, t2) JOIN t3).现在JOIN具有更高的优先级，因此该表达式将被解释为(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.

• Previously, the comma operator (,) and JOIN both had the same precedence, so the join expression t1, t2 JOIN t3 was interpreted as ((t1, t2) JOIN t3). Now JOIN has higher precedence, so the expression is interpreted as (t1, (t2 JOIN t3)). This change affects statements that use an ON clause, because that clause can refer only to columns in the operands of the join, and the change in precedence changes interpretation of what those operands are.

示例:

CREATE TABLE t1 (i1 INT, j1 INT);
CREATE TABLE t2 (i2 INT, j2 INT);
CREATE TABLE t3 (i3 INT, j3 INT);
INSERT INTO t1 VALUES(1,1);
INSERT INTO t2 VALUES(1,1);
INSERT INTO t3 VALUES(1,1);
SELECT * FROM t1, t2 JOIN t3 ON (t1.i1 = t3.i3);

以前，由于t1,t2作为(t1,t2).现在，JOIN具有优先权，因此ON子句的操作数为t2和t3.因为t1.i1都不是两个操作数中的一列，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明确分组，以使ON子句的操作数为(t1,t2)和t3:

Previously, the SELECT was legal due to the implicit grouping of t1,t2 as (t1,t2). Now the JOIN takes precedence, so the operands for the ON clause are t2 and t3. Because t1.i1 is not a column in either of the operands, the result is an Unknown column 't1.i1' in 'on clause' error. To allow the join to be processed, group the first two tables explicitly with parentheses so that the operands for the ON clause are (t1,t2) and t3:

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

或者，避免使用逗号运算符，而改为使用JOIN:

Alternatively, avoid the use of the comma operator and use JOIN instead:

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

此更改还适用于将逗号运算符与INNER JOIN，CROSS JOIN，LEFT JOIN和RIGHT JOIN混合使用的语句，所有这些语句现在都比逗号运算符具有更高的优先级.

This change also applies to statements that mix the comma operator with INNER JOIN, CROSS JOIN, LEFT JOIN, and RIGHT JOIN, all of which now have higher precedence than the comma operator.

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