Two queries optimize
SELECT `type`, COUNT(`id`) AS 'type' FROM `items` WHERE `post` = `id` GROUP BY `type`;
SELECT `type`, COUNT(`post`!=`id`) AS 'posts' FROM `items` GROUP BY `type`;

SELECT  `type`,
        COUNT(`post`=`id`),
        COUNT(`post`!=`id`) AS 'posts'
FROM    `items`
GROUP BY    `type`;