Related page / section:https://developer.matomo.org/guides/database-schema#visit-actions
idaction_event_category andidaction_event_action are missing from this section (whereas they are mentioned inAction Types >Referencing action types section)

idaction_name: the ID of the page title action type for this action in case of page view, of the event name in case of custom event, of the search keyword in case of search event
search_cat: the search category in case of search event
search_count: the number of search results in case of search event
idaction_event_category: the ID of theevent category action type for this action (in case of custom event)
idaction_event_action: the ID of theevent action action type for this action (in case of custom event)

Without this, it is not easy to understand the data model especially thatidaction_name can be used for different types of events...