数据库行列倒置查询语句

CREATE TABLE `demo` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `field_name` varchar(32) NOT NULL COMMENT '字段名称',
  `field_val` text NOT NULL COMMENT '字段值',
  `key`  varchar(32) NOT NULL COMMENT '分组标示',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;
 
/*数据*/
INSERT INTO `demo` VALUES ('1', 'date', '2015-01-01',1);
INSERT INTO `demo` VALUES ('2', 'createtime', '2015-12-30 10:12:12',1);
INSERT INTO `demo` VALUES ('3', 'date', '2015-01-01',3);
INSERT INTO `demo` VALUES ('4', 'createtime', '2015-12-30 12:12:12',2);