POSTS
SELECT YEAR(post_date), COUNT(*)
FROM `wp_posts`
WHERE post_status = 'publish'
GROUP BY YEAR(post_date)
ORDER BY YEAR(post_date)

AVG POST LENGTH
SELECT YEAR(post_date), AVG(LENGTH(post_content))
FROM `wp_posts`
WHERE post_status = 'publish'
GROUP BY YEAR(post_date)
ORDER BY YEAR(post_date)

TOTAL POST LENGTH
SELECT YEAR(post_date), SUM(LENGTH(post_content))
FROM `wp_posts`
WHERE post_status = 'publish'
GROUP BY YEAR(post_date)
ORDER BY YEAR(post_date)

COMMENTS
SELECT YEAR(comment_date), COUNT(*)
FROM `wp_comments`
WHERE comment_approved = '1'
GROUP BY YEAR(comment_date)
ORDER BY YEAR(comment_date)

AVG COMMENTS
SELECT YEAR(post_date), AVG(comment_count)
FROM `wp_posts`
WHERE post_status = 'publish'
GROUP BY YEAR(post_date)
ORDER BY YEAR(post_date)