CODEWITHSUNDEEP
sqlmysql
Pierre Spring
Pierre Spring

Reputation: 10675

MySQL: Union of a Left Join with a Right Join

Say we have the following tables t1 and t2:

t1:
id | column_1
-------------
 1 |   1
 2 |   2

t2:
id | column_2
-------------
 2 |   2
 3 |   3

and we want to find the following result:

id | column_1 | column_2
------------------------
 1 |  1       | 
 2 |  2       | 2
 3 |          | 3

This basically is the union of a right join with a left join. The following code works but feels clumsy:

(
    SELECT t1.id, t1.column_1, t2.column_2 
    FROM t1 
    LEFT JOIN t2 ON t1.id = t2.id
)
UNION
(
    SELECT t2.id, t1.column_1, t2.column_2 
    FROM t1 
    RIGHT JOIN t2 ON t1.id = t2.id
)

Is there a better way to achieve this?

Upvotes: 4

Views: 14457

Answers (3)

Blama
Blama

Reputation: 264

Try this one:

SELECT t1.id, t1.column_1, t2.column_2 
FROM t1 
FULL OUTER JOIN t2 ON (t1.id = t2.id)

Edit: Doesn't work, MySQL does not know FULL OUTER JOIN. Have a look here: http://www.xaprb.com/blog/2006/05/26/how-to-write-full-outer-join-in-mysql/

Upvotes: 1

Alex Weinstein
Alex Weinstein

Reputation: 9891

Haven't tried this myself, but this might work: 

SELECT t1.id, t1.column_1, t2.column_2, t2a.column_2
FROM t1     
LEFT JOIN t2 ON t1.id = t2.id
RIGHT JOIN t2 AS t2a ON t1.id = t2a.id

Upvotes: 0

D'Arcy Rittich
D'Arcy Rittich

Reputation: 171421

select a.id, t1.column_1, t2.column_2
from (
    select id from t1
    union 
    select id from t2
) a
left outer join t1 on a.id = t1.id
left outer join t2 on a.id = t2.id

Upvotes: 10

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