我想为championships
表格中的每个冠军选择当前持有者,并且返回尚未获得任何获胜者的冠军的NULL
。如何为每个锦标赛选择当前持有人?
下面是创建报表的两个表:
CREATE TABLE `championships` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL,
`friendly_name` varchar(255) NOT NULL,
`rank` int(2) unsigned NOT NULL DEFAULT '1',
PRIMARY KEY (`id`),
UNIQUE KEY `name` (`name`),
UNIQUE KEY `friendly_name` (`friendly_name`)
) ENGINE=InnoDB;
CREATE TABLE `title_history` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`championship` int(10) unsigned NOT NULL,
`winner` varchar(255) NOT NULL,
`date_from` date NOT NULL,
`location` varchar(255) NOT NULL,
PRIMARY KEY (`id`),
KEY `championship` (`championship`)
) ENGINE=InnoDB;
ALTER TABLE `title_history` ADD CONSTRAINT `title_history_ibfk_1` FOREIGN KEY (`championship`) REFERENCES `championships` (`id`) ON UPDATE CASCADE;
什么MySQL的语句返回的数据集,我想?
'title_history'表中的'winner'中有什么字符串? – alex 2011-06-13 09:24:39
获胜者的名字,即John Doe。 – 2011-06-13 09:42:03