Question

I have these two tables in my db

describe external_review_sources;
+-------+--------------+------+-----+---------+----------------+
| Field | Type         | Null | Key | Default | Extra          |
+-------+--------------+------+-----+---------+----------------+
| ersID | int(11)      | NO   | PRI | NULL    | auto_increment |
| name  | varchar(50)  | NO   | UNI | NULL    |                |
| logo  | varchar(255) | NO   |     | NULL    |                |
+-------+--------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

And

describe listing_external_review_source_rel;
+---------+--------------+------+-----+---------+----------------+
| Field   | Type         | Null | Key | Default | Extra          |
+---------+--------------+------+-----+---------+----------------+
| lersrID | int(11)      | NO   | PRI | NULL    | auto_increment |
| bid     | int(10)      | NO   |     | NULL    |                |
| url     | varchar(255) | NO   |     | NULL    |                |
| ersID   | int(11)      | YES  |     | NULL    |                |
| active  | int(10)      | NO   |     | NULL    |                |
| order   | int(10)      | NO   |     | NULL    |                |
+---------+--------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)

I query these tables this way:

    SELECT * 
    FROM 
        listing_external_review_source_rel 
        RIGHT JOIN
        external_review_sources USING(ersID)
    where bid=902028 or bid IS NULL;

+-------+---------------+------+---------+--------+-------+--------+-------+
| ersID | name          | logo | lersrID | bid    | url   | active | order |
+-------+---------------+------+---------+--------+-------+--------+-------+
|     1 | G1            | a    |      17 | 902028 | url11 |      1 |     0 |
|     2 | D1            | b    |      18 | 902028 | url22 |      0 |     0 |
+-------+---------------+------+---------+--------+-------+--------+-------+
2 rows in set (0.00 sec)

As you can see results are showing up for bid=902028, how ever for a bid such as 866696 that does NOT exist in listing_external_review_source_rel, the results are empty

SELECT * 
FROM listing_external_review_source_rel 
     RIGHT JOIN external_review_sources USING(ersID) 
where bid=866696  or bid IS NULL;
Empty set (0.00 sec)

I expect the results to be this:

+-------+---------------+------+---------+--------+-------+--------+-------+
| ersID | name          | logo | lersrID | bid    | url   | active | order |
+-------+---------------+------+---------+--------+-------+--------+-------+
|     1 | G1            | NULL |     NULL| NULL   | NULL  |   NULL |  NULL |
|     2 | D1            | NULL |     NULL| NULL   | NULL  |   NULL |  NULL |
+-------+---------------+------+---------+--------+-------+--------+-------+
2 rows in set (0.00 sec)

That’s what I have used the “or bid IS NULL” condition.

What am I doing wrong and what query would give me this result? I basically am interested in having nonmatching rows in my results as well.

Answer 1

Most people use LEFT JOIN so I’ll rewrite it to be more standard:

SELECT *
FROM external_review_sources a LEFT JOIN
     listing_external_review_source_rel b ON a.ersID=b.ersID AND bid=866696;

Remember that an outter join returns all rows where the ON condition matches, and NULL where they don’t. In this case your match condition is more than just the ersID