Question

I have several tables with different numbers and types of columns, and a single column in common.

+--------+---------+------------+-------------+
| person | beardID | beardStyle | beardLength |
+--------+---------+------------+-------------+

+--------+-------------+----------------+
| person | moustacheID | moustacheStyle |
+--------+-------------+----------------+

I want to fetch all the results that match a given value of the shared column. I can do it using multiple select statements like this:

SELECT * FROM beards WHERE person = "bob"

and

SELECT * FROM moustaches WHERE person = "bob"

But this requires multiple mysql API calls, which seems inefficient. I was hoping I could use UNION ALL to get all the results in a single API call, but UNION requires that the tables have the same number and similar type of columns. I could write a SELECT statement that would manually pad the results from each table by adding columns with NULL values, but that would quickly get unmanageable for a few more tables with a few more columns.

I’m looking for a result set roughly like this:

+--------+---------+------------+-------------+-------------+----------------+
| person | beardID | beardStyle | beardLength | moustacheID | moustacheStyle |
+--------+---------+------------+-------------+-------------+----------------+
| bob    | 1       | rasputin   | 1           |             |                |
+--------+---------+------------+-------------+-------------+----------------+
| bob    | 2       | samson     | 12          |             |                |
+--------+---------+------------+-------------+-------------+----------------+
| bob    |         |            |             | 1           | fu manchu      |
+--------+---------+------------+-------------+-------------+----------------+

Is there a way to achieve this that’s fast and maintainable? Or am I better off running a separate query for each table?

Clarification:

I’m not looking for a cartesian product. I don’t want a row for every combination of beard-and-moustache, I want a row for every beard and a row for every moustache.

So if there are 3 matching beards and 2 matching moustaches I should get 5 rows, not 6.

Answer 1

this should be working fine:

SELECT * FROM `beards` b LEFT OUTER JOIN `mustaches` ON (0) WHERE  person = "bob"
UNION ALL
SELECT * FROM `beards` b RIGHT OUTER JOIN `mustaches` ON (0) WHERE  person = "bob"

you don’t have to handle the columns by yourself. the left and right outer join do this job.
unfortunately mysql doesn’t have a full join. that’s why you have to do it this way with a union

SELECT * FROM `customer` b LEFT OUTER JOIN `charges` ON (0) LEFT OUTER JOIN `day` ON (0)
UNION
SELECT * FROM `customer` b RIGHT OUTER JOIN `charges` ON (0) LEFT OUTER JOIN `day` ON (0)
UNION
SELECT * FROM `customer` b LEFT OUTER JOIN `charges` ON (0) RIGHT OUTER JOIN `day` ON (0)

this is a local test i made