About
An outer join is a join that links two tables, one of which has rows that do not match those in the common column of the other table. More …
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Definition
You define an outer join by specifying which table is the outer table in the original equi-join. The outer table contains the column for which you want to return all values, even if they are unmatched. You specify the outer table from the Edit Join dialog box for the selected join.
Left or Right Outer join
What is a SQL Left (Outer) Join?, SQL - Right Outer Join
Designer displays the join in the Structure pane. The outer join is indicated by a small circle on the opposite side of the join to the table that returns unmatched values.