If you have the Data Explorer plugin installed on your site, you can get details about the number codes used by hovering over the entries:
For example, hovering over the posts post_type field shows the following values:
- regular: 1
- moderator action: 2
- small action: 3
- whisper: 4
Other than the Data Explorer, the only place I know of to find this information is in the Discourse code. For example, to find the meaning of each action_type from the user_actions table, enter UserAction.types at the Rails console. That returns the following values:
{:like=>1, :was_liked=>2, :bookmark=>3, :new_topic=>4, :reply=>5, :response=>6, :mention=>7, :quote=>9, :edit=>11, :new_private_message=>12, :got_private_message=>13, :solved=>15, :assigned=>16}