Is there a simple way to merge two wp_posts tables while avoiding duplicates?
Import the new table as
wp_posts_2, then join them and delete all duplicates based on post_content; then merge the two tables.
The following SQL query (untested!) should give the posts from the new table to be deleted:
SELECT wp2.* FROM wp_posts_2 as wp2 LEFT JOIN wp_posts as wp ON wp2.post_content = wp.post_content WHERE wp2.post_content = wp.post_content
So, you can delete the entries with this query (also untested):
DELETE wp_posts_2.* LEFT JOIN wp_posts as wp ON wp_posts_2.post_content = wp.post_content WHERE wp_posts_2.post_content = wp.post_content
Then merge the two tables.