How can a FULL JOIN operation be performed using only standard SQL queries without the direct operator?

The FULL JOIN operation can be emulated using the union of the results of LEFT JOIN and RIGHT JOIN with UNION, excluding duplicate rows.

Example in SQL:

SELECT a.*, b.*
FROM tableA a
LEFT JOIN tableB b ON a.id = b.id
UNION
SELECT a.*, b.*
FROM tableA a
RIGHT JOIN tableB b ON a.id = b.id;

This query combines all rows from both tables, matching them based on the join condition, and includes rows that do not have a match in the other table.