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When somebody has configured there MySQL server with sql_mode ONLY_FULL_GROUP_BY enabled, Piwik chrashes all the time with errors that there are columns SELECTed which aren't specified in the GROUP BY.
I've created a small patch which can detect this setting on the MySQL server and configures the connection Piwik uses, to use the default sql_mode in order to make Piwik work like expected.
Attachment: This patch detects ONLY_FULL_GROUP_BY and disables it.
I'd rather fix whatever SQL query is causing the error.
(In ) fixes #1733 - add non-aggregated columns to GROUP BY clause
I am seeing this issue again in Piwik 1.11.1 and MariaDB 5.5.30 with ONLY_FULL_GROUP_BY enabled. Removing the ONLY_FULL_GROUP_BY option from sql_mode made Piwik work properly again.
Can you create a new bug for your problem and post the full error message and more information.