Can you tell the difference between an inner join and an outer join?

An inner join returns only the rows that have matching keys in both tables. If a row in either table has no counterpart in the other, it is excluded from the result set. An outer join expands on this by including unmatched rows as well. A left outer join keeps all rows from the left table and adds matching rows from the right; unmatched right rows become NULL. A right outer join does the opposite, keeping all rows from the right table. A full outer join keeps all rows from both tables, filling missing side values with NULL. Thus, the key difference is that inner joins filter to only matched rows, while outer joins preserve unmatched rows from one or both sides.