Does MySQL Support Full Outer Joins?

MySQL's Lack of Direct Full Outer Join Support and Workarounds

The Question: Does MySQL offer a native full outer join, ensuring all rows from both joined tables are included regardless of matching criteria?

The Answer: No, MySQL doesn't directly support full outer joins. However, we can effectively replicate this functionality using alternative techniques.

Approach 1: Leveraging UNION

This approach is suitable when there's no risk of generating duplicate rows in the output. The query combines a LEFT JOIN and a RIGHT JOIN using UNION:

<code class="language-sql">SELECT * FROM t1
LEFT JOIN t2 ON t1.id = t2.id
UNION
SELECT * FROM t1
RIGHT JOIN t2 ON t1.id = t2.id;</code>

Approach 2: Employing UNION ALL with Anti-Join

For scenarios where duplicate rows are possible, a more robust method is needed. This involves using UNION ALL along with an anti-join to eliminate redundancy:

<code class="language-sql">SELECT * FROM t1
LEFT JOIN t2 ON t1.id = t2.id
UNION ALL
SELECT * FROM t1
RIGHT JOIN t2 ON t1.id = t2.id
WHERE t1.id IS NULL;</code>

The anti-join (WHERE t1.id IS NULL in the RIGHT JOIN portion) filters out duplicates before the UNION ALL operation combines the results. This ensures a complete and accurate emulation of a full outer join.

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