Catch first img in post, remove it then associate to post as custom field?

Question

In my WordPress blog there are more than 500 posts.

Each post starts with small image.

I want to remove those small images from inside posts and display them as Custom Fields.

It will take me a long time to go through all posts and make the required change.

Is it possible to run a SQL query that will be able to:

1. Catch the small images.
2. Remove the small images from inside the post.
3. Associate small image to a post as a custom field.

Answer 1

I don't think sql could do that. Instead, I'd write a small php script that does something like this (in pseudo code, you'll need to finish this) using a parser I just Googled (http://simplehtmldom.sourceforge.net/):

$post_collection = query('get all posts');

for( $i = 0; $i < $post_collection.length; $i++ ) {
  $html =  str_get_html( $post_collection[$i] );
  $that_first_image = $html->find('img', 1);
  query('save $that_first_image to custom field');
  $html->find('img', 1) = '';
  query('save $html over the old post');
}