plugins/notifications/share/db/sql/notifications.sql.php
<?php
return '
`id` int(11) NOT NULL AUTO_INCREMENT,
`add_date` int(11) NOT NULL,
`receiver_type` enum(\'user_id\',\'admin_id\',\'user_id_tmp\') NOT NULL,
`title` varchar(255) NOT NULL DEFAULT \'\',
`content` text NOT NULL,
PRIMARY KEY (`id`)
';