⚈ it could even include providing alternate spellings or synonyms
`canonical` would also have an index, possibly FULLTEXT and/or utf8mb4_bin. `canonical` may have duplicates even though `exact` probably does not.
Then, when the 'user' searches, you do the same folding to "canonical" before searching `canonical`. Display from `exact`.
LOAD DATA INFILE
In LOAD DATA INFILE, the manual points out: // "The server uses the character set indicated by the character_set_database system variable to interpret the information in the file. SET NAMES and the setting of character_set_client do not affect interpretation of input. If the contents of the input file use a character set that differs from the default, it is usually preferable to specify the character set of the file by using the CHARACTER SET clause. A character set of binary specifies 'no conversion'."
Characters in Western Europe
Taken from Wikipedia
å, ä and ö in Finnish and Swedish à, ç, è, é, ï, í, ò, ó, ú, ü in Catalan å, æ and ø in Norwegian and Danish á, é, ó, ý, è, ë, ï in Dutch ä, ö, ü and ß in German á, ð, í, ó, ú, ý, æ and ø in Faroese á, ð, é, í, ó, ú, ý, þ, æ and ö in Icelandic à, â, ç, è, é, ë, ê, ï, î, ö, ô, ù, û, ÿ, æ, œ in French à, è, é, ì, ò, ù in Italian á, é, í, ñ, ó, ú, ï, ü, ¡, ¿ in Spanish à, á, â, ã, ç, é, ê, í, ó, ô, õ, ú in Portuguese (ü no longer used) á, é, í, ó, ú in Irish £ in British English
Turkish
The columns: utf8, unicode codepoint decimal, hex, HTML entity, 'name':
C387 0199 00C7 Ç latin capital letter c with cedilla C396 0214 00D6 Ö latin capital letter o with diaeresis C39C 0220 00DC Ü latin capital letter u with diaeresis C3A7 0231 00E7 ç latin small letter c with cedilla C3B6 0246 00F6 ö latin small letter o with diaeresis C3BC 0252 00FC ü latin small letter u with diaeresis C49E 0286 011E Ğ latin capital letter g with breve C49F 0287 011F ğ latin small letter g with breve C4B0 0304 0130 İ latin capital letter i with dot above C4B1 0305 0131 ı latin small letter dotless i C59E 0350 015E Ş latin capital letter s with cedilla C59F 0351 015F ş latin small letter s with cedilla E282A4 8356 20A4 ₤ lira sign E282BA 8378 20BA ₺ Turkish lira sign
Don't expect latin1 to work well:
CREATE TABLE `se96265` (
`content` mediumtext NOT NULL,
FULLTEXT KEY `content` (`content`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
SET NAMES utf8;
-- Turkish word for Croatia, second char is \xC4\xB1
INSERT INTO `se96265` (`content`) VALUES ('Hırvatistan');
SELECT content, HEX(content), HEX('Hırvatistan') FROM se96265\G
*************************** 1. row ***************************
content: H?rvatistan
HEX(content): 483F72766174697374616E
HEX('Hırvatistan'): 48C4B172766174697374616E
Note how the 'C4B1' turned into '?'
To get an error:
mysql> SET SESSION sql_mode = 'STRICT_ALL_TABLES'; -- So the INSERT will cause an error:
mysql> INSERT INTO `se96265` (`content`) VALUES ('Hırvatistan');
ERROR 1366 (HY000): Incorrect string value: '\xC4\xB1rvat...' for column 'content' at row 1
(Note: This technique for getting an error message is not specific to Turkish.)
ISO/IEC 8859-9 = latin5 = Turkish
If you have Turkish text in a latin1 column/table, you should convert to latin5 in order to correctly handle the 6 characters that are different (latin1: ÐÝÞðýþ --> latin5 ĞİŞğış). See Stackoverflow
Arabic/Farsi
Arabic characters 2 bytes in utf8: Dxyy. For example, Arabic Letter 'HAH' is D8AD.
To get diacritic insensitive comparisons, use utf8_unicode_ci:
SELECT 'بِسْمِ' = 'بسم' COLLATE utf8_unicode_ci;
The result I got back was 1 (true), meaning they are considered equal.
With utf8_general_ci it came back with 0, meaning not equal.
(Of course, you should declare your column(s) as utf8_unicode_ci rather than using the COLLATE clause.)
Stored Farsi, got '???'
Urdu case folding
Hebrew
To search for a particular character in a string, LIKE or REGEXP will work.
To search for "a cell being entirely Hebrew" is not easy. Essentially, you look for the utf8 encoding, then build a REGEXP to accomodate it. For example, to see which rows have a Hebrew `name` (in utf8):
WHERE HEX(name) REGEXP '^(D7..)+$'
See forum discussionThis assumes (not quite perfectly) that all Hebrew encodings are D7xx. This can be adapted to other languages if the encoding is not to complex. Chinese, for example, is complex:
WHERE HEX(name) REGEXP '^(E.....)+$'
⚈ Chinese characters are 3 bytes (6 hex) long
⚈ This fails to handle the 4-byte Chinese characters
⚈ This includes Japanese, Cherokee, etc.
If you have the "hebrew" encoding in a latin1 column, you may need a 3-step ALTER. See stackoverflow
Storing Hebrew strings Ok, but gibberish when pulling data on another server
Cyrillic, Macedonian, etc
(Random notes)
Cyrillic in utf8 is encoded D0yy-D4yy and EA99yy-EA9Ayy, but perhaps only D0yy is in common use.
For Cyrillic: utf8_unicode_ci is fine for these languages: Russian, Bulgarian, Belarusian, Macedonian, Serbian, and Ukrainian. While utf8_general_ci is fine only for Russian and Bulgarian subset of Cyrillic. Extra letters used in Belarusian, Macedonian, Serbian, and Ukrainian are sorted not well.
`Ќ` is hex `D08C` in utf8 or utf8mb4. Cyrillic is completely covered by either `CHARACTER SET`. `К` is `D09A`. Hmmm, this is quite interesting:
mysql> SELECT 'К' = 'Ќ' COLLATE utf8_bin AS bin, 'К' = 'Ќ' COLLATE utf8_general_ci AS general, 'К' = 'Ќ' COLLATE utf8_unicode_ci AS unicode; +-----+---------+---------+ | bin | general | unicode | +-----+---------+---------+ | 0 | 1 | 0 | +-----+---------+---------+f
mysql> SELECT 'Г' = 'Ѓ' COLLATE utf8_bin AS bin, 'Г' = 'Ѓ' COLLATE utf8_general_ci AS general, 'Г' = 'Ѓ' COLLATE utf8_unicode_ci AS unicode; +-----+---------+---------+ | bin | general | unicode | +-----+---------+---------+ | 0 | 1 | 0 | +-----+---------+---------+
And if it helps, here's the method from the alphabet helper. def alphabet cyrillic_alphabet = ["А", "Б", "В", "Г", "Д", "Ѓ", "Е", "Ж", "З", "Ѕ", "И", "Ј", "К", "Л", "Њ", "М", "Н", "Љ", "О", "П", "Р", "С","Т", "Ќ", "У", "Ф", "Х", "Ц", "Ч", "Џ", "Ш"] end – NewbieOnRails yesterday
These are letters in Macedonian alphabet, not on the Ubuntu Cyrillic keyboard.
⚈ D086 1030=x0406 [І] L CYRILLIC CAPITAL LETTER BYELORUSSIAN-UKRAINIAN I
⚈ D087 1031=x0407 [Ї] L CYRILLIC CAPITAL LETTER YI
⚈ D08B 1035=x040B [Ћ] L CYRILLIC CAPITAL LETTER TSHE
⚈ D08E 1038=x040E [Ў] L CYRILLIC CAPITAL LETTER SHORT U
The bit patterns are different, so utf8_bin collates unequal. But usually whenever general is equal, so is unicode. Cyrillic/Macedonian
Cyrillic example: title: Добро пожаловать в Диксон, hex: D094D0BED0B1D180D0BE20D0BFD0BED0B6D0B0D0BBD0BED0B2D0B0D182D18C20D0B220D094D0B8D0BAD181D0BED0BD, length: 47, char length: 25
Data entry of Cyrillic in Workbench yields "????"
Other Natural Languages
This is a list hits about natural languages. Most have not been verified.
Lithuanian ąĄ čČ ęĘ ėĖ įĮ ųŲ ūŪ are saved as ?, however, šŠ žŽ do get saved. The reason: Column declared latin1
Vietnamese collations were added in MySQL 5.6.
em dash, dagger, and other special characters
mysql> SELECT ';' semicolon, UNHEX('cdbe') 'Greek question mark';
+-----------+---------------------+
| semicolon | Greek question mark |
+-----------+---------------------+
| ; | ; |
+-----------+---------------------+
cp1250 - Central Europe
For a Devanagari character range:
SELECT 'क़ज़फ़' REGEXP '^[क़-फ़]+$'; --> trueStackoverflow thread
UTF8 Chinese String Comparison
Python
1st or 2nd line in source code (to have literals in the code utf8-encoded): # -*- coding: utf-8 -*-
Python code for dumping hex (etc) for string 'u':
for i, c in enumerate(u):
print i, '%04x' % ord(c), unicodedata.category(c),
print unicodedata.name(c)
Miscellany notes on coding for utf8:
⚈ db = MySQLdb.connect(host=DB_HOST, user=DB_USER, passwd=DB_PASS, db=DB_NAME, charset="utf8", use_unicode=True)
⚈ conn = MySQLdb.connect(host="localhost", user='root', password='', db='', charset='utf8')
⚈ config = { ..., 'charset': 'utf8', ... }
⚈ cursor.execute("SET NAMES utf8mb4;") -- not as good as using `charset'
⚈ db.set_character_set('utf8'), implies use_unicode=True
⚈ Literals should be u'...'
⚈ MySQL-python 1.2.4 fixes a bug wherein varchar(255) CHARACTER SET utf8 COLLATE utf8_bin is treated like a BLOB.
Checklist:
⚈ `# -*- coding: utf-8 -*-` -- (for literals in code)
⚈ `charset='utf8'` in `connect()` call -- Is that buried in `bottle_mysql.Plugin`? (Note: Try 'utf-8' and 'utf8')
⚈ Text encoded in utf8.
⚈ No need for encode() or decode() if you are willing to accept utf8 everywhere.
⚈ `u'...'` for literals
⚈ <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> near start of html page
⚈ <meta charset="utf-8" /> is a shorter version (if using only HTML5).
⚈ Content-Type: text/html; charset=UTF-8 (in HTTP response header)
⚈ header('Content-Type: text/html; charset=UTF-8'); (in PHP to get that response header)
⚈ `CHARACTER SET utf8 COLLATE utf8_general_ci` on column (or table) definition in MySQL.
⚈ utf8 all the way through
⚈ Use MySQL Connector/Python instead of pyodbc and MySQL Connector/ODBC
Side note: Python defaults to autocommit=off; this can be a rude surprise when your INSERTs vanish.
References:
⚈ https://docs.python.org/2/howto/unicode.html#the-unicode-type
⚈ http://stackoverflow.com/questions/9154998/python-encoding-mysql
⚈ http://dev.mysql.com/doc/connector-python/en/connector-python-connectargs.html
⚈ http://stackoverflow.com/questions/34069603/python-pyodbc-weird-unicode-bytecode
How to store arabic text in mysql database using python?
The Python language environment officially only uses UCS-2 internally since version 2.0, but the UTF-8 decoder to "Unicode" produces correct UTF-16. Since Python 2.2, "wide" builds of Unicode are supported which use UTF-32 instead;[16] these are primarily used on Linux. Python 3.3 no longer ever uses UTF-16, instead strings are stored in one of ASCII/Latin-1, UCS-2, or UTF-32, depending on which code points are in the string, with a UTF-8 version also included so that repeated conversions to UTF-8 are fast.
Python check for utf8 (versus utf8mb4)
The python package "MySQL-python" version needs to be at least 1.2.5 in order to handle utf8mb4.
PHP
Random notes about PHP. (See also Best Practice, above.)
In php.ini: default_charset UTF-8 The default changed to UTF-8 in PHP 5.6.
To see what PHP has:
$hex = unpack('H*', $text);
echo implode('', $hex);
or simply echo bin2hex($text);
To get "U+" (unicode) notation, first fetch the data, then use PHP code trim(str_replace('\u', ' U+', json_encode('كتب عربية')), '" '); This will result in U+0643 U+062a U+0628 U+0639 U+0631 U+0628 U+064a U+0629.
PHP: Convert \unnnn to utf8:
$myr = '\u101c\u1031\u1011'; // Given this
$x = json_decode('"'.$myr.'"'); // Add quotes and decode
// $x is not string, like လေထ
If you use header(), do: header('Content-type: text/plain; charset=utf-8');
PHP: undo_magic_quotes_gpc($_POST);
BjyProfiler needs charset=utf8; it apparently overrides other PHP settings.
Other Computer Languages
This is a list of hints on how to establish utf8 for various computer languages. Most have not been verified.
Drupal, WordPress, and any other product that uses PHP: Turn off mbstring.encoding_translation. Probably everything to do with mbstring should be avoided.
AJAX
Apache servers are (were?) configured to serve files in ISO-8859-1 by default, so you need to add the following line to your .htaccess file:
AddDefaultCharset UTF-8
ASP, ASP.Net
<%Response.charset="utf-8"%>
Connector/C
mysql_set_character_set('utf8mb4');
C#: C# code to undo (while reading?) double-encoded strings
Similar code in SQL:
CONVERT(UNHEX(HEX(CONVERT(CONVERT(col USING utf8) USING latin1))), CHAR)Put this in the connection string:
id=my_user;password=my_password;database=some_db123;charset=utf8;Lao and C#
codeigniter:
application/config/config.php :
$config['charset'] = 'UTF-8';application/config/database.php :
'char_set' => 'utf8', 'dbcollat' => 'utf8_general_ci',
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs, HTTP.UTF_8));
echo meta('Content-type', 'text/html; charset=utf-8', 'equiv');
In database.php, Set char_set to utf8mb4 and dbcollat to utf8mb4_unicode_ci or utf8_general_ci Codeigniter 3.0 notes
ColdFusion
<cfprocessingdirective pageEncoding="utf-8">
<cffile
action="read"
file="#settings.csvfile#"
variable="autodata"
charset="utf-8">
Django needs client_encoding: 'UTF8' Django utf8 usage
ucs2 versus utf16
Java originally used UCS-2, and added UTF-16 supplementary character support in J2SE 5.0.
⚈ What if you put a 5.1 slave off a 4.x master? (The German sharp-s could cause trouble.)
⚈ Replication type (SBR vs RBR)?
Add ?useUnicode=yes&characterEncoding=UTF-8 to the JDBC URL
<%@ page language="java" pageEncoding="UTF-8"%> <%@ page contentType="text/html;charset=UTF-8" %> compileJava.options.encoding = 'UTF-8'
<form method="post" action="/your/url/" accept-charset="UTF-8">
To use 4-byte UTF8 with Connector/J configure the MySQL server with character_set_server=utf8mb4. Connector/J will then use that setting as long as characterEncoding has not been set in the connection string. This is equivalent to autodetection of the character set.
Drupal
amending your settings.php database connection by adding:
$databases['default']['default'] = array(
'driver' => 'mysql',
'database' => 'databasename',
'username' => 'username',
'password' => 'password',
'host' => 'localhost',
'charset' => 'utf8mb4',
'collation' => 'utf8mb4_general_ci',
);
More discussion of utf8mb4
Jetty
jetty
Grails Grails and utf8mb4
Java Servlet
resource.setContentType ("text/html;charset=utf-8");
JSP
<%@ page contentType="text/html; charset=UTF-8" %>
node.js var connection = mysql.createConnection({ ... , charset : 'utf8mb4'}); stackoverflow
NET
Server=myServerAddress;Database=myDataBase;Uid=myUsername;Pwd=myPassword;CharSet=utf8;
Powershell ISE and Powershell Console: $OutputEncoding = New-Object -typename System.Text.UTF8Encoding
library(RODBC)
imp <- odbcConnect("SERVER", uid = "***", pwd="***",DBMSencoding="utf8")
ODBC 3.5.1 probably won't handle utf8; either of these may be correct:
ODBC;DRIVER={MySQL ODBC 5.1 Driver};UID=...;PWD=...;PORT=3306;DATABASE=...;SERVER=127.0.0.1;CHARSET=UTF8;
strConnection="driver={MySQL ODBC 5.1 Driver}; server=...;uid=...;pwd=...;database=...;stmt=SET NAMES utf8;"
Unicode is not supported in ADO applications (including ASP) with the Connector/ODBC 3.51 driver. Please consider testing MySQL Connector/ODBC 5.1 which includes Unicode support for ASP.
Perl:
use utf8;
use open ':std', ':encoding(UTF-8)';
my $dbh = DBI->connect("dbi:mysql:".$dsn, $user, $password, {
PrintError => 0,
RaiseError => 1,
mysql_enable_utf8 => 1, # Switch to UTF-8 for communication and decode.
});
# or {mysql_enable_utf8mb4 => 1} if using utf8mb4
Stackoverflow - double encoding and JSONPHP see above
pymysql:
import pymysql
con = pymysql.connect(host='127.0.0.1', port=3306,
user='root', passwd='******',
charset="utf8")
Python see above
R / RStudio
Tool -> Global Options -> Code -> Saving and put UTF-8 rs <- dbSendQuery(con, 'set character set "utf8"') rs <- dbSendQuery(con, 'SET NAMES utf8')
Rails: Rails and utf8mb4
Ruby on Rails:
"\xD0\x9A\xD0\xB0\xD1\x81\xD0\xBB".force_encoding("UTF-8") => "Щасл"
Watch out for rake db:reset . Consider, instead, rake db:drop && rake db:create && rake db:migrate . The reset just created the tables from the already stored schema which had the wrong charset and collation. But re-creating them from the migrations created them with the new charset and collation.
RoR: application_controller.rb
def configure_charsets
response.headers["Content-Type"] = "text/html; charset=utf-8"
suppress(ActiveRecord::StatementInvalid) do
ActiveRecord::Base.connection.execute 'SET NAMES UTF8'
end
end
Edit your database.yml with below code line encoding: utf8
Spring/Hibernate: (See also Best Practice, above.)
Spring/Hibernate filter:
<form accept-charset="UTF-8">
Spring/Hibernate: <property name="url" value="jdbc:mysql://localhost:3306/miniprojetjee?useUnicode=true&connectionCollation=utf8_general_ci&characterSetResults=utf8&characterEncoding=utf-8"/>
"Spring": @RequestMapping(value = "/getRegion2", produces={"application/json; charset=UTF-8"},method = RequestMethod.GET)
Hibernate manual
Spring MVC UTF-8 Encoding
encoding-filter org.springframework.web.filter.CharacterEncodingFilter encoding UTF-8 forceEncoding true
Spring Boot
sqlalchemy:
db_url = sqlalchemy.engine.url.URL(drivername='mysql', host=foo.db_host,
database=db_schema,
query={ 'read_default_file' : foo.db_config, 'charset': 'utf8mb4' })
MySQL-Unicode in sqlalchemyTomcat
[[http://stackoverflow.com/questions/13504732/how-to-use-org-springframework-web-filter-characterencodingfilter-to-correct-cha][tomcat]
Wildfly: Configuration -> Subsystems -> Undertow -> Servlet/JSP -> View -> Set "User listener encoding" to true.
WordPress: wp-config.php, define('DB_CHARSET', 'utf8mb4'); and define('DB_COLLATE', ''); WordPress & utf8mb4
vb.net / VBScript:
Dim MyConn As New MySqlConnection("Server=localhost;User Id=u;Password=x;Database=d;Charset=utf8")
<%@language="VBSCRIPT" CODEPAGE="65001" LCID=1033%>
web.xml
web.xml
Random notes
UTF-8 all the way through
Scan for 8-bit codes, find and decipher double-encoding
A table declared to be latin1, and containing latin1 bytes can be converted to utf8 via
ALTER TABLE tbl CONVERT TO CHARACTER SET utf8;
Example from forumsUsing Replication to assist in charset conversion?
utf8_general_ci, which will treat Résumé the same as resume MYSQL doesn't 'see' accents
Exact match when _ci collation is on column - even using index
WHERE keyword = CONVERT('cho' USING binary)
Re: constants in SQL:
EXPLAIN EXTENDED SELECT ...; SHOW WARNINGS;sometimes gives extra clues into what charset/collation issues are being faced during a SELECT. It will probably contain 'introducers'; example: _utf8'abc'.
To ponder: convert(convert((binary col1) using latin1) using utf8)
phpMyAdmin might be connecting as "root", thereby bypassing init_connect = "SET NAMES utf8". This could defeat your attempts to be fully utf8. Possible workaround: Use a login that avoids SUPER priv. (This suggestion is good advice for all applications -- for security reasons.)
# Find rows with any 8-bit chars:
SELECT * FROM tbl WHERE HEX(colname) RLIKE '^(..)*[8-F].';
# Remove all occurrences of one 8-bit code (hex 92, in this example):
UPDATE tbl SET colname = REPLACE(colname, UNHEX('92'), '');
Reference:
how to replace hex in varchar fieldConverting latin1 hex to utf8 hex: HEX(CONVERT(CONVERT(UNHEX('F6') USING LATIN1) USING UTF8)) ⇒ C3B6
Adding a Character Set or Collation
(Note: The doc refers to version 5.5, but probably applies to all versions from 4.1 on.)
Connector/.NET possibly defaults to latin1. Consider changing 'connection string' if you need utf8.
Suggested for my.cnf by stackoverflow
[client] default-character-set=utf8 [mysql] default-character-set=utf8 character-set-server = utf8 [mysqld] collation-server = utf8_unicode_ci init-connect='SET NAMES utf8' character-set-server = utf8
Caution: Setting default-character-set that way for the mysql client cannot be overridden by SET NAMES.
my.cnf: skip-character-set-client-handshake to pretend to be 4.0?
A possible double-encoding fix
$string = htmlspecialchars($string, ENT_QUOTES, "UTF-8");
my.cnf needs these to force the server and the client to use UTF8:
skip-character-set-client-handshake collation-server=utf8_unicode_ci character-set-server=utf8However, "The server character set and collation are used as default values if the database character set and collation are not specified in CREATE DATABASE statements. They have no other purpose." manual on charset-server
It is not clear whether skip-character-set-client-handshake is really needed.
For a description of the character_set_* settings and SET NAMES: manual on Connection Character Sets
In 5.6, this helps get Unicode rendering for mysql commandline tool for Windows: mysql --default-character-set=utf8 Windows Unicode Support
Also sugest (in my.ini)
[mysql] default-character-set=utf8
<?xml version="1.0" encoding="utf-8"?>
REGEXP (RLIKE) with character class is likely to work wrong: Bug report from 2007
Manual Warning
<form method="post" action="/your/url/" accept-charset="UTF-8">
Changing default charset
Possible values for <meta http-equiv="Content-Type" content="text/html; charset=..." /> can be found in iana charsets
For example, use 'ISO-8859-9' for MySQL's 'latin5'.
How to fix a table that has a mixture of latin1 and utf8
Test for Chinese characters: REGEXP '^(..)*(E[2-9F]|F0A)' -- Caveat: This may not be precise. StackOverflow discussion
In my.cnf:
collation_server = utf8mb4_unicode_520_cisets
character_set_database | utf8mb4 character_set_server | utf8mb4 collation_database | utf8mb4_unicode_520_ci collation_server | utf8mb4_unicode_520_cibut not the things set by SET NAMES, nor collation_connection.
From language name to list of characters (dwell to see unicode, not utf8)
Illustrive examples of ALTERs
5.5.3 (10/2010) Changelog: The following obsolete constructs have been removed. The --default-character-set and --default-collation server options (use --character-set-server and --collation-server). Then...
5.7.6 (9/2015) Changelog: The following items are deprecated and will be removed in a future MySQL release. The global character_set_database and collation_database system variables are deprecated and will be removed in a future version of MySQL. Assigning a value to the session character_set_database and collation_database system variables is deprecated and assignments produce a warning. The session variables will become read only in a future version of MySQL and assignments will produce an error. It will remain possible to access the session variables to determine the database character set and collation for the default database.
LOAD DATA added syntax to include charset valid for the file to be loaded. In 4.1, LOAD DATA utilises database charset. Bug 10195
Footnote
If this solves your problem, please let me know. My ego needs a pat on the back. If it does not solve your problem, please contact me, maybe I can pull as special rabbit out of my hat, just for you.
Original writing -- Sep 2010, after struggling with hundreds of questions both in-house and from the forums. Alas, this does not achieve the ultimate goal of "Given this symptom, do that". (See 2015) I hope it helps most people.
Revision date: 2012-08-26 (This document continues to evolve as more problems and examples are discovered.)
Revision date: 2013-02-12 (Misc, plus added 8-bit encodings)
Revision date: 2015-March/April Finally getting close to "If you see this, this is what happened, and here's how to fix it". Add better summary of what errors occur and how to fix them. Add/fix several links.
Revision date: 2016-01-25 Shuffled language info.
Contact me by posting a question at MySQL Forums :: Character Sets, Collation, Unicode
-- Rick James
MySQL Documents by Rick James
HowTo Techniques for Optimizing Tough Tasks:Partition Maintenance (DROP+REORG) for time series (includes list of PARTITION uses)
Big DELETEs - how to optimize -- and other chunking advice, plus a use for PARTITIONing
Chunking lengthy DELETE/UPDATE/etc.
Data Warehouse techniques:
Overview Summary Tables High speed ingestion
Entity-Attribute-Value -- a common, poorly performing, design pattern (EAV); plus an alternative
Find the nearest 10 pizza parlors -- efficient searching on Latitude + Longitude (another PARITION use)
Pagination, not with OFFSET, LIMIT
Techniques on efficiently finding a random row (On beyond ORDER BY RAND())
GUID/UUID Performance (type 1 only)
IP Range Table Performance -- or other disjoint ranges
Rollup Unique User Counts
Alter of a Huge table -- Mostly obviated by 5.6
Latest 10 news articles -- how to optimize the schema and code for such
Build and execute a "Pivot" SELECT (showing rows as columns)
Find largest row for each group ("groupwise max")
Other Tips, Tuning, Debugging, Optimizations, etc...
Rick's RoTs (Rules of Thumb -- lots of tips)
Memory Allocation (caching, etc)
Character Set and Collation problem solver
Converting from MyISAM to InnoDB -- includes differences between them
Compound INDEXes plus other insights into the mysteries of INDEXing
Cookbook for Creating Indexes
Many-to-many mapping table
MySQL Limits -- built-in hard limits
Galera, tips on converting to (Percona XtraDB Cluster, MariaDB 10, or manually installed)
5.7's Query Rewrite -- perhaps 5.7's best perf gain, at least for this forum's users
Best of MySQL Forum -- index of lots of tips, discussions, etc
