I see galleries are represented as separate post records with post_type = 'gallery' in the database.
How is this record (gallery) associated with a basic post (type = 'post') in the terms of database records?
WordPress gallery and post association in database
The post type “gallery” is not a default post type of WordPress so this must be a custom post type in your case.
Custom post types are also stored in the wp_posts table.
This link may explain more: http://codex.wordpress.org/Post_Types
I hope this answers your question. If you need more clarification, please be specific.