WordPress. How to merge two Posts and Comments

A question on existing WordPress installations, and how to merge some comments together into one post.

Scenario:

Two separate WordPress sites are to be joined together as one, as each has similar or identical posts, but each has there own individual, different, comments.

Result needed:

One site, one of each posts, but ALL comments added to the one remaining post.

How to do it:

Using the WordPress Export and Import functions, we can easily do the Export/Import bit, even by category, and then we have ALL the posts in one site.

Then comes the hard bit, the merging, but I will try and see if it works.

I read this instruction to merge the comments from post1 to post2:

Using phpMyAdmin, in the wp_comments table, find any record that has a comment_post_ID equal to the post ID for post1 and change it to the post ID value for post2.

This entails doing each post individually…. Not good if you have hundreds off posts.