rss feeds from two tables and to come on top the latest created in two tables

hii all

want to generate rss feeds from two tables and to come on top the
latest created in two tables

1st table

create table
CREATE TABLE `content_masters` (
`id` int(11) NOT NULL auto_increment,
`image_path` varchar(255) collate utf8_unicode_ci default NULL,
`content_text` text collate utf8_unicode_ci,
`abstract_text` varchar(700) collate utf8_unicode_ci default NULL,
`title` varchar(255) collate utf8_unicode_ci default NULL,
`color` varchar(255) collate utf8_unicode_ci default NULL,
`parent_id` int(11) default NULL,
`promote` int(11) default '0',
`promote_block` varchar(255) collate utf8_unicode_ci default 'N',
`draft_state` varchar(255) collate utf8_unicode_ci default 'N',
`order_no_article` int(11) default NULL,
`created_at` datetime default NULL,
`updated_at` datetime default NULL,
`photo_file_name` varchar(255) collate utf8_unicode_ci default NULL,
`photo_content_type` varchar(255) collate utf8_unicode_ci default
NULL,
`photo_file_size` int(11) default NULL,
`photo_updated_at` datetime default NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=29 DEFAULT CHARSET=utf8
COLLATE=utf8_unicode_ci

create table
CREATE TABLE `sub_content_masters` (
`id` int(11) NOT NULL auto_increment,
`abstract_text` varchar(700) collate utf8_unicode_ci default NULL,
`title` varchar(255) collate utf8_unicode_ci default NULL,
`image_id` varchar(255) collate utf8_unicode_ci default NULL,
`order_no` int(11) default NULL,
`created_at` datetime default NULL,
`updated_at` datetime default NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8
COLLATE=utf8_unicode_ci

want to join these two table in query
so that i got the latest created , title with abstract_text