I just imported my entries from my blog into a freshly installed Wordpress. I created a new user..e.g. "bob" (bob has an ID=2 in the wp_users table). I want the author of the new posts that I've imported to be "bob". So I thought that I change the post_author of a post to 2! However, when I went to view the post in the blog, the author was still the old author. I found the work around for this...you can actually change the author by using the bulk post editing function. After I did this, the posts in the blog had their author as "bob".
But, when I went to the wp_posts table, the post_author field did not change. I looked at all the wp_ tables and can't see where a post's author is indicated. The only place that I found was the wp_posts table...but changing the post_author doesn't see to take any effect when you look at the blog.
So, the mystery is...where is the real author id of a post kept?
OK...I found out that there were some posts that were duplicated except for their 'post_status'. There are some weird statuses such as 'auto-save' and 'inherit'. I unfortunately didn't see the post_status column and changed the 'post_author' of a post with the 'inherit' status.
So mystery solved... The new mystery, i.e. what the different 'post_status' values are is answered here.