Why FULL OUTER JOIN?

FULL OUTER JOIN displays every row from each table in the join clause.
This join is helpful when you want to find unmatched row when there is no relation between the tables (no relation integraty).




So if there are foreign key constrains on the join column the FULL OUTER JOIN provide result set as LEFT OUTER JOIN clause.
In Addition, when foreign key constrains are defined, an OUTER JOIN defined with the primary key table being defined as the outer table provides the same results as an INNER JOIN.