How to create a post thumbnail from images in an article in WP for already published posts?

Question

SQL

Good afternoon! Recently migrated a database from a DLE website to WordPress. The problem is that before there were no thumbnails, and my theme and overall design concept suggests them. Manually not an option, about 10,000 entries published. I tried the Auto Post Thumbnail plugin, but it worked extremely poorly (thumbnails appeared only in 5%, about records).
Please give me ideas how to do it. Thank you!
PS Whether it is possible to make it SQL request?

Answer 1

I usually use this plugin - https://wordpress.org/plugins/quick-featured-images/
But the functionality you need - the first image from the article as a thumbnail is available in the premium version.
The second option - if you export articles through WP All Import, then there is an opportunity to select the first image as a thumbnail