MySql 将多条查询记录合并为一条记录
GROUP_CONCAT()示例：//表结构 CREATE TABLE `demo` ( `id` int(11) unsigned NOT NULL AUTO_INCREMENT, `a` int(11) DEFAULT '0', `b` varchar(50) DEFAULT '', PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREME
GROUP_CONCAT()示例：//表结构 CREATE TABLE `demo` ( `id` int(11) unsigned NOT NULL AUTO_INCREMENT, `a` int(11) DEFAULT '0', `b` varchar(50) DEFAULT '', PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREME