We've said it before, but let's say it again: An outer join returns all the data from the left or right side of a join — you specify which side — and only matching data from the other side. For example, if your boss wants to know which products haven't sold, an outer join can give you that data.
You create an outer join by editing the properties of a join.
Open your query in Design view, right-click the join line, and click Join Properties
In the Join Properties
dialog box, select either the second or third options. Option two creates a left outer join, meaning the query returns all the data from the base table on the left side of the join, and only the matching records from the secondary table on the right. Option three does just the opposite, creating a right outer join.
You can always spot an outer join, because Access displays them as arrows.