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 -- ------------------------------------------------------------------ Charles Cazabon <charlesc-web-register-launchpad.net@pyropus.ca> Software, consulting, and services available at http://pyropus.ca/ ------------------------------------------------------------------