mysql MERGE 异常(differently defined or of non-MyISAM type)

mysql MERGE 错误(differently defined or of non-MyISAM type)
错误代码：
Error Code : 1168
Unable to open underlying table which is differently defined or of non-MyISAM type or doesn't exist

出现这样的错误原因是：
表结构不一样或者表字段没有包含varchar类型。
如：

CREATE TABLE `allwebsite` (                                                                                                                       `id` int(11) NOT NULL AUTO_INCREMENT,                                                                                                               `siteBigType` int(11) DEFAULT NULL,                                                                                                                                                                              `siteSmallType` int(11) DEFAULT NULL,                                                                                                                                                             `siteWorth` varchar(15) DEFAULT '0' COMMENT '网站价值',                                                                                              `date` date DEFAULT NULL,                                                                                                             index(`id`)               )ENGINE=MERGE UNION=(website0001,website0002) INSERT_METHOD=LAST AUTO_INCREMENT=1 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci