You can use any of the grouping functions in your select expression. Their values will be calculated based on all the rows that have been grouped together for each result row. If you select a non-grouped column or a value computed from a non-grouped column, it is undefined which row the returned value is taken from. This is not permitted if the ONLY_FULL_GROUP_BY SQL_MODE is used.
orry many mails
" The server is free to choose any value from each group, so unless they are the same, the values chosen are indeterminate. "
2014-05-23 15:32 GMT-03:00 Roberto Spadim <roberto@spadim.com.br>:
http://dev.mysql.com/doc/refman/5.6/en/group-by-extensions.html
here, but must check if mariadb have something like it2014-05-23 15:21 GMT-03:00 Roberto Spadim <roberto@spadim.com.br>:
maybe you should use something like MIN() MAX(), since you are using a GROUP BYi don't know if this is well documented but i think it's2014-05-23 15:18 GMT-03:00 Charles Cazabon <charlesc-web-register-launchpad.net@pyropus.ca>: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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