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MariaDB server is a community developed fork of MySQL server. Started by core members of the original MySQL team, MariaDB actively works with outside developers to deliver the most featureful, stable, and sanely licensed open SQL server in the industry.
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CAN LEAD TO MISSING TABLES Overview -------- If the FOREIGN_KEY_CHECKS system variable is set to 0, it is possible to break a foreign key constraint by changing the type or character set of the foreign key column, or by dropping the foreign key index (without carrying out corresponding changes on another table in the relationship). If we subsequently set FOREIGN_KEY_CHECKS to 1 and execute ALTER TABLE involving the COPY algorithm on such a table, the following happens: 1) If ALTER TABLE does not contain a RENAME clause, the attempt to install the new version of the table instead of the old one will fail due to the fact that the inconsistency will be detected. An attempt to revert the partially executed alter table operation by restoring the old table definition will fail as well due to FOREIGN_KEY_CHECKS == 1. As a result, the table being altered will be lost. 2) If ALTER TABLE contains the RENAME clause, the inconsistency will not be detected (most probably due to other bugs). But if an attempt to install the new version of the table fails (for example, due to a failure when updating triggers associated with the table), reverting the partially executed alter table by restoring the old table definition will fail too. So the table being altered might be lost as well. Suggested fix ------------- The suggested fix is to temporarily unset the option bit representing FOREIGN_KEY_CHECKS when the old table definition is restored while reverting the partially executed operation. |
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MySQL Server 5.5 This is a release of MySQL, a dual-license SQL database server. For the avoidance of doubt, this particular copy of the software is released under the version 2 of the GNU General Public License. MySQL is brought to you by Oracle. Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved. License information can be found in the COPYING file. MySQL FOSS License Exception We want free and open source software applications under certain licenses to be able to use specified GPL-licensed MySQL client libraries despite the fact that not all such FOSS licenses are compatible with version 2 of the GNU General Public License. Therefore there are special exceptions to the terms and conditions of the GPLv2 as applied to these client libraries, which are identified and described in more detail in the FOSS License Exception at <http://www.mysql.com/about/legal/licensing/foss-exception.html>. This distribution may include materials developed by third parties. For license and attribution notices for these materials, please refer to the documentation that accompanies this distribution (see the "Licenses for Third-Party Components" appendix) or view the online documentation at <http://dev.mysql.com/doc/>. GPLv2 Disclaimer For the avoidance of doubt, except that if any license choice other than GPL or LGPL is available it will apply instead, Oracle elects to use only the General Public License version 2 (GPLv2) at this time for any software where a choice of GPL license versions is made available with the language indicating that GPLv2 or any later version may be used, or where a choice of which version of the GPL is applied is otherwise unspecified. For further information about MySQL or additional documentation, see: - The latest information about MySQL: http://www.mysql.com - The current MySQL documentation: http://dev.mysql.com/doc Some Reference Manual sections of special interest: - If you are migrating from an older version of MySQL, please read the "Upgrading from..." section. - To see what MySQL can do, take a look at the features section. - For installation instructions, see the Installing and Upgrading chapter. - For the new features/bugfix history, see the MySQL Change History appendix. You can browse the MySQL Reference Manual online or download it in any of several formats at the URL given earlier in this file. Source distributions include a local copy of the manual in the Docs directory.