A database operation with a view or query that links the rows in two or more tables or views by comparing the values in specified fields. For example, the default join between tables is an inner join that selects records from both tables only when the values of the joined fields are equal. Because SQL is based on mathematical set theory, each table can be represented as a circle. The join condition determines the point of overlap which represents the set of records that match. This overlap occurs within the interior or "inner" portion of the two circles. An outer join includes not only those matched rows found in the inner cross section of the tables, but also the rows in the outer part of the circle to the left, or right, of the intersection.