Eight tasks across the intermediate skills, several needing two at once, as real questions do. Keep the habits: unnest arrays to work with their elements, use the event_params subquery for GA4 parameters, filter wildcard tables with _TABLE_SUFFIX, and give window sorts a tie-breaker.
Build each query at the requested grain before adding a second skill. A purchase item is not a session, and an event parameter can be missing even when its event exists. Keep a left-side row when the task asks for zeroes, and use a deterministic tie rule when it asks for one result. The hidden copy changes counts and values, so explain the rule in SQL rather than copying a displayed number.