sql

SELECT `threads`.`id`, `threads`.`name`, COALESCE(`posts`.`date`, `threads`.`date`) AS `date`
FROM `threads`
LEFT JOIN (
    SELECT `posts`.`tothread`, `posts`.`date`
    FROM `posts`
    ORDER BY `date` DESC
) AS `posts`
    ON `posts`.`tothread` = `threads`.`id`
GROUP BY `name`
ORDER BY `date` DESC