mirror of
https://github.com/MariaDB/server.git
synced 2025-01-26 08:44:33 +01:00
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.
amazon-web-servicesdatabasefulltext-searchgalerageographical-information-systeminnodbjsonmariadbmysqlrdbmsrelational-databasessqlstorage-enginevector-database
0e787b245b
Consider the following query:
SELECT f_1,..,f_m, AGGREGATE_FN(C)
FROM t1
WHERE ...
GROUP BY ...
Loose index scan ("Using index for group-by") can be used for
this query if there is an index 'i' covering all fields in the
select list, and the GROUP BY clause makes up a prefix f1,...,fn
of 'i'. Furthermore, according to rule NGA2 of
get_best_group_min_max(), the WHERE clause must contain a
conjunction of equality predicates for all fields fn+1,...,fm.
The problem in this bug was that a query with WHERE clause that
broke NGA2 was not detected and therefore used loose index scan.
This lead to wrong result. The query had an index
covering (c1,c2) and had:
"WHERE (c1 = 1 AND c2 = 'a') OR (c1 = 2 AND c2 = 'b')
GROUP BY c1"
or
"WHERE (c1 = 1 ) OR (c1 = 2 AND c2 = 'b')
GROUP BY c1"
This WHERE clause cannot be transformed to a conjunction of
equality predicates.
The solution is to introduce another rule, NGA3, that complements
NGA2. NGA3 says that if a gap field (field between those
listed in GROUP BY and C in the index) has a predicate, then
there can only be one range in the query. This requirement is
more strict than it has to be in theory. BUG 15947433 will deal
with that.
|
||
|---|---|---|
| .bzr-mysql | ||
| BitKeeper | ||
| BUILD | ||
| client | ||
| cmd-line-utils | ||
| config/ac-macros | ||
| dbug | ||
| Docs | ||
| extra | ||
| include | ||
| libmysql | ||
| libmysql_r | ||
| libmysqld | ||
| man | ||
| mysql-test | ||
| mysys | ||
| netware | ||
| plugin | ||
| regex | ||
| scripts | ||
| server-tools | ||
| sql | ||
| sql-bench | ||
| sql-common | ||
| storage | ||
| strings | ||
| support-files | ||
| tests | ||
| unittest | ||
| vio | ||
| win | ||
| zlib | ||
| .bzrignore | ||
| .cvsignore | ||
| CMakeLists.txt | ||
| configure.in | ||
| COPYING | ||
| INSTALL-SOURCE | ||
| INSTALL-WIN-SOURCE | ||
| Makefile.am | ||
| README | ||
MySQL Server 5.1 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.