SELECT M.msg_id, M.uid_fk, M.message, M.created,
U.fname, U.lname, M.uploads
FROM messages M, users_friends F, users U
WHERE M.uid_fk=F.friendID
and F.userID = '5'
and status='2'
建造一堵类似Facebook的墙,想从朋友那里获取消息(更新(。
上面的查询返回一个空集,即使我已经确保表中有来自用户 5 的消息。
图式:
CREATE TABLE IF NOT EXISTS `messages` (
`msg_id` int(11) NOT NULL AUTO_INCREMENT,
`message` varchar(200) CHARACTER SET utf8 DEFAULT NULL,
`uid_fk` int(11) DEFAULT NULL,
`ip` varchar(30) DEFAULT NULL,
`created` int(11) DEFAULT '1269249260',
`uploads` varchar(30) DEFAULT NULL,
PRIMARY KEY (`msg_id`),
KEY `uid_fk` (`uid_fk`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=263 ;
CREATE TABLE IF NOT EXISTS `users` (
`fname` varchar(15) NOT NULL,
`lname` varchar(15) NOT NULL,
`userID` int(11) NOT NULL AUTO_INCREMENT,
`username` varchar(23) NOT NULL,
`email` varchar(50) NOT NULL,
`password` varchar(32) NOT NULL,
`DOB` date DEFAULT NULL,
`sex` varchar(1) DEFAULT NULL,
`about` text NOT NULL,
`location` varchar(20) DEFAULT NULL,
`last_login` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
`user_level` int(11) NOT NULL DEFAULT '0',
`profile_image` varchar(200) NOT NULL,
`profile_image_small` varchar(200) NOT NULL,
PRIMARY KEY (`userID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=19 ;
CREATE TABLE IF NOT EXISTS `users_friends` (
`userID` int(11) NOT NULL,
`friendID` int(11) NOT NULL,
`status` int(1) NOT NULL DEFAULT '0',
PRIMARY KEY (`userID`,`friendID`),
KEY `fk_users_has_friends_users1` (`userID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
您在 WHERE 子句中单引 → '5' 和 '2' 中的 INT 值。
另外,请尝试加入。
SELECT M.msg_id,
M.uid_fk,
M.message,
M.created,
U.fname,
U.lname,
M.uploads
FROM messages M
INNER JOIN users_friends F ON F.friendID = M.uid_fk
AND F.userID = 5
AND F.status = 2
INNER JOIN users U ON U.userID = F.friendID;