我有一个查询应该是检索用户的朋友。
鉴于我们所处的情况,我们user two
对查询sent
的请求user one
应返回 的帐户信息user one
。(这种情况的 SQLfiddle)[正常工作]
鉴于我们的情况,我们user one
来自recieved
查询的请求user two
应该返回 的帐户信息user two
。(本场景的 SQLfiddle)[返回空结果]
因此,只要我们是发送请求的用户,查询就可以正常工作,但是如果我们是接收请求的用户,它就不起作用。
我可以通过切换 JOIN、LEFT => RIGHT
、来解决这个问题RIGHT => LEFT
。但这打破了第一种情况。
我可以解决两个查询的联合问题。(这个场景的 SQLfiddle)但肯定不是最有效的方法。所以,基本问题:我应该如何创建这个查询?
情景一:
SELECT `accounts`.*,
IFNULL(`f1`.`sender`, `f2`.`sender`) AS `sender`,
IFNULL(`f1`.`recipient`, `f2`.`recipient`) AS `recipient`,
IFNULL(`f1`.`date_sent`, `f2`.`date_sent`) AS `date_sent`,
IFNULL(`f1`.`date_reviewed`, `f2`.`date_reviewed`) AS `date_reviewed`,
IFNULL(`f1`.`accepted`, `f2`.`accepted`) AS `accepted`
FROM `accounts`
LEFT JOIN `friendships` AS `f1` ON `accounts`.`id` = `f1`.`sender`
RIGHT JOIN `friendships` AS `f2` ON `accounts`.`id` = `f2`.`recipient`
WHERE (`f1`.`recipient` = 2 OR `f2`.`sender` = 2);
修补场景二
SELECT `accounts`.*,
IFNULL(`f1`.`sender`, `f2`.`sender`) AS `sender`,
IFNULL(`f1`.`recipient`, `f2`.`recipient`) AS `recipient`,
IFNULL(`f1`.`date_sent`, `f2`.`date_sent`) AS `date_sent`,
IFNULL(`f1`.`date_reviewed`, `f2`.`date_reviewed`) AS `date_reviewed`,
IFNULL(`f1`.`accepted`, `f2`.`accepted`) AS `accepted`
FROM `accounts`
RIGHT JOIN `friendships` AS `f1` ON `accounts`.`id` = `f1`.`sender`
LEFT JOIN `friendships` AS `f2` ON `accounts`.`id` = `f2`.`recipient`
WHERE (`f1`.`recipient` = 2 OR `f2`.`sender` = 2);
为两种情况工作(问题基本上是;没有工会我怎么能做到这一点?):
SELECT `accounts`.*,
IFNULL(`f1`.`sender`, `f2`.`sender`) AS `sender`,
IFNULL(`f1`.`recipient`, `f2`.`recipient`) AS `recipient`,
IFNULL(`f1`.`date_sent`, `f2`.`date_sent`) AS `date_sent`,
IFNULL(`f1`.`date_reviewed`, `f2`.`date_reviewed`) AS `date_reviewed`,
IFNULL(`f1`.`accepted`, `f2`.`accepted`) AS `accepted`
FROM `accounts`
LEFT JOIN `friendships` AS `f1` ON `accounts`.`id` = `f1`.`sender`
RIGHT JOIN `friendships` AS `f2` ON `accounts`.`id` = `f2`.`recipient`
WHERE (`f1`.`recipient` = 1 OR `f2`.`sender` = 1)
UNION
SELECT `accounts`.*,
IFNULL(`f1`.`sender`, `f2`.`sender`) AS `sender`,
IFNULL(`f1`.`recipient`, `f2`.`recipient`) AS `recipient`,
IFNULL(`f1`.`date_sent`, `f2`.`date_sent`) AS `date_sent`,
IFNULL(`f1`.`date_reviewed`, `f2`.`date_reviewed`) AS `date_reviewed`,
IFNULL(`f1`.`accepted`, `f2`.`accepted`) AS `accepted`
FROM `accounts`
RIGHT JOIN `friendships` AS `f1` ON `accounts`.`id` = `f1`.`sender`
LEFT JOIN `friendships` AS `f2` ON `accounts`.`id` = `f2`.`recipient`
WHERE (`f1`.`recipient` = 1 OR `f2`.`sender` = 1);
架构创建:
CREATE TABLE `accounts` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`status` tinyint(4) DEFAULT '0',
`type` varchar(25) NOT NULL,
`username` varchar(25) NOT NULL,
`first_name` varchar(80) NOT NULL,
`last_name` varchar(80) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=latin1;
/*Data for the table `accounts` */
insert into `accounts`
(`id`,`status`,`type`,`username`,`first_name`,`last_name`)
values
(1,1,'writer','user1','User','One'),
(2,1,'writer','user2','User','Two'),
(3,1,'publisher','user3','User','Three');
CREATE TABLE `friendships` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`sender` int(11) NOT NULL,
`recipient` int(11) NOT NULL,
`date_sent` datetime DEFAULT NULL,
`date_reviewed` datetime DEFAULT NULL,
`accepted` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=latin1;
/*Data for the table `friendships` */
insert into `friendships`
(`id`,`sender`,`recipient`,`date_sent`,`date_reviewed`,`accepted`)
values (3,2,1,'2013-07-16 20:54:46',NULL,NULL);