How to Work Around MySQL's Lack of FULL OUTER JOIN Support?

Solving MySQL's FULL OUTER JOIN Limitation

MySQL's lack of native FULL OUTER JOIN support often leads to syntax errors. This guide demonstrates a workaround using the UNION operator to achieve the same result.

Encountering this error:

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'outer join airports on airlines.iaco_code = airports.iaco_code
  full outer join' at line 4

confirms MySQL's incompatibility with the FULL OUTER JOIN statement.

The solution involves simulating a FULL OUTER JOIN using UNION for two or more tables.

Two Tables (t1 and t2):

SELECT * FROM t1
LEFT JOIN t2 ON t1.id = t2.id
UNION
SELECT * FROM t1
RIGHT JOIN t2 ON t1.id = t2.id

This combines the results of a LEFT JOIN (all rows from t1, matching rows from t2) and a RIGHT JOIN (all rows from t2, matching rows from t1), effectively replicating a FULL OUTER JOIN.

Three Tables (t1, t2, and t3):

For three tables, the complexity increases, requiring multiple UNION operations:

SELECT * FROM t1
LEFT JOIN t2 ON t1.id = t2.id
LEFT JOIN t3 ON t2.id = t3.id
UNION
SELECT * FROM t1
RIGHT JOIN t2 ON t1.id = t2.id
LEFT JOIN t3 ON t2.id = t3.id
UNION
SELECT * FROM t1
RIGHT JOIN t2 ON t1.id = t2.id
RIGHT JOIN t3 ON t2.id = t3.id

This approach systematically combines all possible join combinations to emulate a FULL OUTER JOIN across three tables. Remember to adjust t1.id and t2.id to reflect the actual join columns in your specific scenario. This technique allows you to bypass MySQL's limitations and achieve the desired FULL OUTER JOIN functionality.

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