4941ac9192
(Variant#3: Allow cross-charset comparisons, use a special CHARSET_INFO to create lookup keys. Review input addressed.) Equalities that compare utf8mb{3,4}_general_ci strings, like: WHERE ... utf8mb3_key_col=utf8mb4_value (MB3-4-CMP) can now be used to construct ref[const] access and also participate in multiple-equalities. This means that utf8mb3_key_col can be used for key-lookups when compared with an utf8mb4 constant, field or expression using '=' or '<=>' comparison operators. This is controlled by optimizer_switch='cset_narrowing=on', which is OFF by default. IMPLEMENTATION Item value comparison in (MB3-4-CMP) is done using utf8mb4_general_ci. This is valid as any utf8mb3 value is also an utf8mb4 value. When making index lookup value for utf8mb3_key_col, we do "Charset Narrowing": characters that are in the Basic Multilingual Plane (=BMP) are copied as-is, as they can be represented in utf8mb3. Characters that are outside the BMP cannot be represented in utf8mb3 and are replaced with U+FFFD, the "Replacement Character". In utf8mb4_general_ci, the Replacement Character compares as equal to any character that's not in BMP. Because of this, the constructed lookup value will find all index records that would be considered equal by the original condition (MB3-4-CMP). Approved-by: Monty <monty@mariadb.org> |
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VERSION |
Code status:
MariaDB: The open source relational database
MariaDB was designed as a drop-in replacement of MySQL(R) with more features, new storage engines, fewer bugs, and better performance.
MariaDB is brought to you by the MariaDB Foundation and the MariaDB Corporation. Please read the CREDITS file for details about the MariaDB Foundation, and who is developing MariaDB.
MariaDB is developed by many of the original developers of MySQL who now work for the MariaDB Corporation, the MariaDB Foundation and by many people in the community.
MySQL, which is the base of MariaDB, is a product and trademark of Oracle Corporation, Inc. For a list of developers and other contributors, see the Credits appendix. You can also run 'SHOW authors' to get a list of active contributors.
A description of the MariaDB project and a manual can be found at:
https://mariadb.com/kb/en/mariadb-vs-mysql-features/
https://mariadb.com/kb/en/mariadb-versus-mysql-compatibility/
https://mariadb.com/kb/en/new-and-old-releases/
Help
More help is available from the Maria Discuss mailing list https://launchpad.net/~maria-discuss, MariaDB's Zulip instance, https://mariadb.zulipchat.com/
Live QA for beginner contributors
MariaDB has a dedicated time each week when we answer new contributor questions live on Zulip. From 8:00 to 10:00 UTC on Mondays, and 10:00 to 12:00 UTC on Thursdays, anyone can ask any questions they’d like, and a live developer will be available to assist.
New contributors can ask questions any time, but we will provide immediate feedback during that interval.
Licensing
NOTE:
MariaDB is specifically available only under version 2 of the GNU General Public License (GPLv2). (I.e. Without the "any later version" clause.) This is inherited from MySQL. Please see the README file in the MySQL distribution for more information.
License information can be found in the COPYING file. Third party license information can be found in the THIRDPARTY file.
Bug Reports
Bug and/or error reports regarding MariaDB should be submitted at: https://jira.mariadb.org
For reporting security vulnerabilities see: https://mariadb.org/about/security-policy/
The code for MariaDB, including all revision history, can be found at: https://github.com/MariaDB/server