Problem in move Pages to Posts within the WP database

Hi,

My main problem is the appearance of slugs in the pages URL (because of the pages hierarchy). The reason for removing the slugs is SEO.

After digging a while I figured out I should move ALL of my 300 pages to posts, and use WP No Category Base plugin to remove the category.

I found out I can use an SQL query to set all page as posts, by using:
UPDATE wordpress.wp_posts SET post_type = 'posts' WHERE post_type = 'page';

after running the query all page disappeared, but did NOT appeared as posts (nothing there)!

Please help with my problems…
Thanks!