Understanding FULL OUTER JOIN and How to Simulate It in MySQL
A FULL OUTER JOIN returns all rows from both tables — matching rows are joined, and non-matching rows from each side are filled with NULL. MySQL does not support FULL OUTER JOIN directly, but it can be simulated using a combination of LEFT JOIN, RIGHT JOIN, and UNION.
• Return all matching rows between two tables.
• Include non-matching rows from the left table (as in LEFT JOIN).
• Include non-matching rows from the right table (as in RIGHT JOIN).
• Fill missing columns with NULL for unmatched rows.
• MySQL's query engine lacks native support for FULL OUTER JOIN.
• MySQL developers emphasize simpler join models (INNER, LEFT, RIGHT).
• FULL OUTER JOIN can be emulated using existing features, so it was never added.
• Combine LEFT JOIN and RIGHT JOIN using UNION.
• UNION ensures duplicates (matching rows) are not repeated.
• Sometimes UNION ALL is preferred for performance.
• Then remove duplicates where matches exist.
In summary: MySQL does not support FULL OUTER JOIN directly, but you can reliably simulate it using a UNION of LEFT JOIN and RIGHT JOIN queries.