The full outer joins help to combine the results of both the right and the left outer join, which means that the resulted table contains all the records from both the table and invoking nulls to the records that have missing values.
Let’s have look at the structure of full outer join and how it is implemented in Mysql:
Consider two table Employ and Student:
SELECT * FROM Employ
LEFT JOIN Student ON Employ.age = Student.age
UNION
SELECT * FROM Employ
RIGHT JOIN Student ON Employ.age = Student.age
The query will give you a result implementing full join and provide the joined table with distinct (does not contain duplicate value)records.
If you change the UNION keyword with UNION ALL, then it will return all the records including duplicate values.
