Hi!
>From MySQL documentation:
http://dev.mysql.com/doc/refman/5.6/en/group-by-extensions.html
"MySQL extends the use of GROUP BY so that the select list can refer to nonaggregated columns not named in the GROUP BY clause. (...) However, this is useful primarily when all values in each nonaggregated column not named in the GROUP BY are the same for each group. The server is free to choose any value from each group, so unless they are the same, the values chosen are indeterminate."
This is the reason why I think that the ONLY_FULL_GROUP_BY sql_mode flag should always be on.
In your specific case, I note that album_id is not in GROUP BY and is not passed to any aggregating function (such as MAX()).
Regards
Federico
--------------------------------------------
El vie, 23/5/14, Charles Cazabon <charlesc-web-register-launchpad.net@pyropus.ca> escribió:
Asunto: [Maria-discuss] query result inconsistency between MariaDB 10.0.x and Oracle MySQL 5.1.x
Para: "MariaDB discuss" <maria-discuss@lists.launchpad.net>
Fecha: viernes, 23 de mayo, 2014 20:18
Greetings,
I recently upgraded the db server behind an application from
MySQL 5.1.73 (as
shipped in Ubuntu 10.04 "Lucid") to MariaDB 10.0.11 (from
the MariaDB repo).
A colleague of mine found an inconsistency between the
results produced by the
two servers for a given query. What we don't know is,
is this a bug (I gather
Maria is aiming at 100% compatibility), or is this somehow
due to the query
relying on unspecified behaviour (that the two db servers
are therefore free
to optimize differently)?
The query is:
SELECT t1.id, t2.album_id
FROM t1
LEFT OUTER JOIN t2
ON t1.data_id = t2.id
AND t1.event_type IN (1002, 1001,
1000)
WHERE
t1.event_type IN (1000, 1001, 1002, 1200,
1201, 1202, 1203)
GROUP BY t1.id
ORDER BY t1.id DESC
LIMIT 0, 20;
The MariaDB result looks like this:
+-----+----------+
| id | album_id |
+-----+----------+
| 623 | NULL |
| 622 | NULL |
| 621 | NULL |
| 620 | NULL |
| 619 | NULL |
| 618 | NULL |
| 617 | NULL |
| 616 | NULL |
| 615 | NULL |
| 614 | NULL |
| 613 | NULL |
| 612 | 194 |
| 611 | NULL |
| 610 | NULL |
| 609 | NULL |
| 608 | 193 |
| 607 | NULL |
| 606 | NULL |
| 605 | NULL |
| 604 | NULL |
+-----+----------+
And the Oracle MySQL result looks like this:
+-----+----------+
| id | album_id |
+-----+----------+
| 623 | NULL |
| 622 | NULL |
| 621 | NULL |
| 620 | NULL |
| 619 | NULL |
| 618 | NULL |
| 617 | NULL |
| 616 | 196 |<-- different
| 615 | NULL |
| 614 | NULL |
| 613 | NULL |
| 612 | 194 |
| 611 | 194 |<-- different
| 610 | NULL |
| 609 | NULL |
| 608 | 193 |
| 607 | 193 |<-- different
| 606 | NULL |
| 605 | NULL |
| 604 | NULL |
+-----+----------+
My colleague pointed out that if you EXPLAIN the queries,
you can see that the
two databases are interpreting the query differently -- see
the "Extra"
column. I can't paste the explain output here without
using very long lines,
so I've pastebinned it:
http://pastebin.com/n2sbH0kY
My colleague has made the data from these tables available
here:
https://dl.dropboxusercontent.com/u/7755033/fatdrop/test_case_data.sql
We've found workarounds for this, but we're really wondering
if we've found a
problem (either in MariaDB-MySQL consistency, or in the
query, or ... ?).
Any assistance appreciated.
Charles
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Charles Cazabon <charlesc-web-register-launchpad.net@pyropus.ca>
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