A.11.1. |
What CJK character sets are available in MySQL?
|
|
The list of CJK character sets may vary depending on your MySQL
version. For example, the gb18030 character
set is not supported prior to MySQL 5.7.4. However, since the
name of the applicable language appears in the
DESCRIPTION column for every entry in the
INFORMATION_SCHEMA.CHARACTER_SETS
table, you can obtain a current list of all the non-Unicode CJK
character sets using this query:
mysql> SELECT CHARACTER_SET_NAME, DESCRIPTION
FROM INFORMATION_SCHEMA.CHARACTER_SETS
WHERE DESCRIPTION LIKE '%Chin%'
OR DESCRIPTION LIKE '%Japanese%'
OR DESCRIPTION LIKE '%Korean%'
ORDER BY CHARACTER_SET_NAME;
+--------------------+---------------------------------+
| CHARACTER_SET_NAME | DESCRIPTION |
+--------------------+---------------------------------+
| big5 | Big5 Traditional Chinese |
| cp932 | SJIS for Windows Japanese |
| eucjpms | UJIS for Windows Japanese |
| euckr | EUC-KR Korean |
| gb18030 | China National Standard GB18030 |
| gb2312 | GB2312 Simplified Chinese |
| gbk | GBK Simplified Chinese |
| sjis | Shift-JIS Japanese |
| ujis | EUC-JP Japanese |
+--------------------+---------------------------------+
(For more information, see
Section 28.3.4, “The INFORMATION_SCHEMA CHARACTER_SETS Table”.)
MySQL supports three variants of the
GB (Guojia
Biaozhun, or National
Standard, or Simplified Chinese)
character sets which are official in the People's Republic of
China: gb2312, gbk, and
(as of MySQL 5.7.4) gb18030.
Sometimes people try to insert gbk characters
into gb2312, and it works most of the time
because gbk is a superset of
gb2312. But eventually they try to insert a
rarer Chinese character and it does not work. (For an example,
see Bug #16072).
Here, we try to clarify exactly what characters are legitimate
in gb2312 or gbk, with
reference to the official documents. Please check these
references before reporting gb2312 or
gbk bugs:
It is also possible to store CJK characters in Unicode character
sets, although the available collations may not sort characters
quite as you expect:
The utf8 and ucs2
character sets support the characters from Unicode Basic
Multilingual Plane (BMP). These characters have code point
values between U+0000 and
U+FFFF.
The utf8mb4, utf16,
utf16le, and utf32
character sets support BMP characters, as well as
supplementary characters that lie outside the BMP.
Supplementary characters have code point values between
U+10000 and U+10FFFF.
The collation used for a Unicode character set determines the
ability to sort (that is, distinguish) characters in the set:
Collations based on Unicode Collation Algorithm (UCA) 4.0.0
distinguish only BMP characters.
Collations based on UCA 5.2.0 or 9.0.0 distinguish BMP and
supplementary characters.
Non-UCA collations may not distinguish all Unicode
characters. For example, the utf8mb4
default collation is utf8mb4_general_ci,
which distinguishes only BMP characters.
Moreover, distinguishing characters is not the same as ordering
them per the conventions of a given CJK language. Currently,
MySQL has only one CJK-specific UCA collation,
gb18030_unicode_520_ci (which requires use of
the non-Unicode gb18030 character set).
For information about Unicode collations and their
differentiating properties, including collation properties for
supplementary characters, see
Section 12.10.1, “Unicode Character Sets”.
|
A.11.2. |
I have inserted CJK characters into my table. Why does
SELECT display them as
“?” characters?
|
|
This problem is usually due to a setting in MySQL that does not
match the settings for the application program or the operating
system. Here are some common steps for correcting these types of
issues:
Be certain of what MySQL version you are
using.
Use the statement SELECT VERSION(); to
determine this.
Make sure that the database is actually using the
desired character set.
People often think that the client character set is always
the same as either the server character set or the character
set used for display purposes. However, both of these are
false assumptions. You can make sure by checking the result
of SHOW CREATE TABLE
tablename or, better
yet, by using this statement:
SELECT character_set_name, collation_name
FROM information_schema.columns
WHERE table_schema = your_database_name
AND table_name = your_table_name
AND column_name = your_column_name;
Determine the hexadecimal value of the character
or characters that are not being displayed
correctly.
You can obtain this information for a column
column_name in the table
table_name using the following
query:
SELECT HEX(column_name)
FROM table_name;
3F is the encoding for the
? character; this means that
? is the character actually stored in the
column. This most often happens because of a problem
converting a particular character from your client character
set to the target character set.
Make sure that a round trip is possible. When you
select literal (or
_introducer hexadecimal-value),
do you obtain literal as a
result?
For example, the Japanese Katakana character
Pe (ペ')
exists in all CJK character sets, and has the code point
value (hexadecimal coding) 0x30da. To
test a round trip for this character, use this query:
SELECT 'ペ' AS `ペ`; /* or SELECT _ucs2 0x30da; */
If the result is not also ペ, the round
trip failed.
For bug reports regarding such failures, we might ask you to
follow up with SELECT HEX('ペ');. Then
we can determine whether the client encoding is correct.
Make sure that the problem is not with the browser
or other application, rather than with MySQL.
Use the mysql client program to
accomplish this task. If mysql displays
characters correctly but your application does not, your
problem is probably due to system settings.
To determine your settings, use the
SHOW VARIABLES statement,
whose output should resemble what is shown here:
mysql> SHOW VARIABLES LIKE 'char%';
+--------------------------+----------------------------------------+
| Variable_name | Value |
+--------------------------+----------------------------------------+
| character_set_client | utf8 |
| character_set_connection | utf8 |
| character_set_database | latin1 |
| character_set_filesystem | binary |
| character_set_results | utf8 |
| character_set_server | latin1 |
| character_set_system | utf8 |
| character_sets_dir | /usr/local/mysql/share/mysql/charsets/ |
+--------------------------+----------------------------------------+
These are typical character-set settings for an
international-oriented client (notice the use of
utf8 Unicode) connected to a server in
the West (latin1 is a West Europe
character set).
Although Unicode (usually the utf8
variant on Unix, and the ucs2 variant on
Windows) is preferable to Latin, it is often not what your
operating system utilities support best. Many Windows users
find that a Microsoft character set, such as
cp932 for Japanese Windows, is suitable.
If you cannot control the server settings, and you have no
idea what setting your underlying computer uses, try
changing to a common character set for the country that
you're in (euckr = Korea;
gb18030, gb2312 or
gbk = People's Republic of China;
big5 = Taiwan; sjis,
ujis, cp932, or
eucjpms = Japan; ucs2
or utf8 = anywhere). Usually it is
necessary to change only the client and connection and
results settings. The SET
NAMES. statement changes all three at once. For
example:
SET NAMES 'big5';
Once the setting is correct, you can make it permanent by
editing my.cnf or
my.ini. For example you might add lines
looking like these:
[mysqld]
character-set-server=big5
[client]
default-character-set=big5
It is also possible that there are issues with the API
configuration setting being used in your application; see
Why does my GUI front end or browser not display
CJK characters correctly...? for more
information.
|
A.11.3. |
What problems should I be aware of when working with the Big5
Chinese character set?
|
|
MySQL supports the Big5 character set which is common in Hong
Kong and Taiwan (Republic of China). The MySQL
big5 character set is in reality Microsoft
code page 950, which is very similar to the original
big5 character set.
A feature request for adding HKSCS extensions
has been filed. People who need this extension may find the
suggested patch for Bug #13577 to be of interest.
|
A.11.4. |
Why do Japanese character set conversions fail?
|
|
MySQL supports the sjis,
ujis, cp932, and
eucjpms character sets, as well as Unicode. A
common need is to convert between character sets. For example,
there might be a Unix server (typically with
sjis or ujis) and a
Windows client (typically with cp932).
In the following conversion table, the ucs2
column represents the source, and the sjis,
cp932, ujis, and
eucjpms columns represent the destinations;
that is, the last 4 columns provide the hexadecimal result when
we use CONVERT(ucs2) or we assign
a ucs2 column containing the value to an
sjis, cp932,
ujis, or eucjpms column.
Now consider the following portion of the table.
This means that MySQL converts the NOT SIGN
(Unicode U+00AC) to sjis
code point 0x81CA and to
cp932 code point 3F.
(3F is the question mark (“?”.
This is what is always used when the conversion cannot be
performed.)
|
A.11.5. |
What should I do if I want to convert SJIS
81CA to cp932?
|
|
Our answer is: “?”. There are disadvantages to
this, and many people would prefer a “loose”
conversion, so that 81CA (NOT SIGN) in
sjis becomes 81CA (FULLWIDTH NOT
SIGN) in cp932.
|
A.11.6. |
How does MySQL represent the Yen (¥) sign?
|
|
A problem arises because some versions of Japanese character
sets (both sjis and euc)
treat 5C as a
reverse solidus
(\, also known as a backslash), whereas
others treat it as a yen sign (¥).
MySQL follows only one version of the JIS (Japanese Industrial
Standards) standard description. In MySQL,
5C is always the reverse solidus
(\).
|
A.11.7. |
Of what issues should I be aware when working with Korean
character sets in MySQL?
|
|
In theory, while there have been several versions of the
euckr (Extended
Unix Code Korea) character set, only one problem has
been noted. We use the “ASCII” variant of EUC-KR,
in which the code point 0x5c is REVERSE
SOLIDUS, that is \, instead of the
“KS-Roman” variant of EUC-KR, in which the code
point 0x5c is WON SIGN
(₩). This means that you cannot convert
Unicode U+20A9 to euckr:
mysql> SELECT
CONVERT('₩' USING euckr) AS euckr,
HEX(CONVERT('₩' USING euckr)) AS hexeuckr;
+-------+----------+
| euckr | hexeuckr |
+-------+----------+
| ? | 3F |
+-------+----------+
|
A.11.8. |
Why do I get Incorrect string value error
messages?
|
|
To see the problem, create a table with one Unicode
(ucs2) column and one Chinese
(gb2312) column.
mysql> CREATE TABLE ch
(ucs2 CHAR(3) CHARACTER SET ucs2,
gb2312 CHAR(3) CHARACTER SET gb2312);
In nonstrict SQL mode, try to place the rare character
汌 in both columns.
mysql> SET sql_mode = '';
mysql> INSERT INTO ch VALUES ('A汌B','A汌B');
Query OK, 1 row affected, 1 warning (0.00 sec)
The INSERT produces a warning.
Use the following statement to see what it is:
mysql> SHOW WARNINGS\G
*************************** 1. row ***************************
Level: Warning
Code: 1366
Message: Incorrect string value: '\xE6\xB1\x8CB' for column 'gb2312' at row 1
So it is a warning about the gb2312 column
only.
mysql> SELECT ucs2,HEX(ucs2),gb2312,HEX(gb2312) FROM ch;
+-------+--------------+--------+-------------+
| ucs2 | HEX(ucs2) | gb2312 | HEX(gb2312) |
+-------+--------------+--------+-------------+
| A汌B | 00416C4C0042 | A?B | 413F42 |
+-------+--------------+--------+-------------+
Several things need explanation here:
The 汌 character is not in the
gb2312 character set, as described
earlier.
If you are using an old version of MySQL, you may see a
different message.
A warning occurs rather than an error because MySQL is not
set to use strict SQL mode. In nonstrict mode, MySQL tries
to do what it can, to get the best fit, rather than give up.
With strict SQL mode, the Incorrect string
value message occurs as an error rather than a
warning, and the INSERT
fails.
|
A.11.9. |
Why does my GUI front end or browser display CJK characters
incorrectly in my application using Access, PHP, or another API?
|
|
Obtain a direct connection to the server using the
mysql client, and try the same query there.
If mysql responds correctly, the trouble may
be that your application interface requires initialization. Use
mysql to tell you what character set or sets
it uses with the statement SHOW VARIABLES LIKE
'char%';. If you are using Access, you are most likely
connecting with Connector/ODBC. In this case, you should check
Configuring Connector/ODBC. If, for example,
you use big5, you would enter SET
NAMES 'big5'. (In this case, no ;
character is required.) If you are using ASP, you might need to
add SET NAMES in the code. Here
is an example that has worked in the past:
<%
Session.CodePage=0
Dim strConnection
Dim Conn
strConnection="driver={MySQL ODBC 3.51 Driver};server=server;uid=username;" \
& "pwd=password;database=database;stmt=SET NAMES 'big5';"
Set Conn = Server.CreateObject("ADODB.Connection")
Conn.Open strConnection
%>
In much the same way, if you are using any character set other
than latin1 with Connector/NET, you must specify the
character set in the connection string. See
Connector/NET Connections, for more
information.
If you are using PHP, try this:
<?php
$link = new mysqli($host, $usr, $pwd, $db);
if( mysqli_connect_errno() )
{
printf("Connect failed: %s\n", mysqli_connect_error());
exit();
}
$link->query("SET NAMES 'utf8'");
?>
In this case, we used SET NAMES
to change character_set_client,
character_set_connection, and
character_set_results.
Another issue often encountered in PHP applications has to do
with assumptions made by the browser. Sometimes adding or
changing a <meta> tag suffices to
correct the problem: for example, to insure that the user agent
interprets page content as UTF-8, include
<meta http-equiv="Content-Type" content="text/html;
charset=utf-8"> in the
<head> section of the HTML page.
If you are using Connector/J, see
Using Character Sets and Unicode.
|
A.11.10. |
I've upgraded to MySQL 8.4. How can I revert to
behavior like that in MySQL 4.0 with regard to character sets?
|
|
In MySQL Version 4.0, there was a single “global”
character set for both server and client, and the decision as to
which character to use was made by the server administrator.
This changed starting with MySQL Version 4.1. What happens now
is a “handshake”, as described in
Section 12.4, “Connection Character Sets and Collations”:
The effect of this is that you cannot control the client
character set by starting mysqld with
--character-set-server=utf8.
However, some Asian customers prefer the MySQL 4.0 behavior. To
make it possible to retain this behavior, we added a
mysqld switch,
--character-set-client-handshake,
which can be turned off with
--skip-character-set-client-handshake.
If you start mysqld with
--skip-character-set-client-handshake,
then, when a client connects, it sends to the server the name of
the character set that it wants to use. However, the
server ignores this request from the client.
By way of example, suppose that your favorite server character
set is latin1. Suppose further that the
client uses utf8 because this is what the
client's operating system supports. Start the server with
latin1 as its default character set:
mysqld --character-set-server=latin1
And then start the client with the default character set
utf8:
mysql --default-character-set=utf8
The resulting settings can be seen by viewing the output of
SHOW VARIABLES:
mysql> SHOW VARIABLES LIKE 'char%';
+--------------------------+----------------------------------------+
| Variable_name | Value |
+--------------------------+----------------------------------------+
| character_set_client | utf8 |
| character_set_connection | utf8 |
| character_set_database | latin1 |
| character_set_filesystem | binary |
| character_set_results | utf8 |
| character_set_server | latin1 |
| character_set_system | utf8 |
| character_sets_dir | /usr/local/mysql/share/mysql/charsets/ |
+--------------------------+----------------------------------------+
Now stop the client, and stop the server using
mysqladmin. Then start the server again, but
this time tell it to skip the handshake like so:
mysqld --character-set-server=utf8 --skip-character-set-client-handshake
Start the client with utf8 once again as the
default character set, then display the resulting settings:
mysql> SHOW VARIABLES LIKE 'char%';
+--------------------------+----------------------------------------+
| Variable_name | Value |
+--------------------------+----------------------------------------+
| character_set_client | latin1 |
| character_set_connection | latin1 |
| character_set_database | latin1 |
| character_set_filesystem | binary |
| character_set_results | latin1 |
| character_set_server | latin1 |
| character_set_system | utf8 |
| character_sets_dir | /usr/local/mysql/share/mysql/charsets/ |
+--------------------------+----------------------------------------+
As you can see by comparing the differing results from
SHOW VARIABLES, the server
ignores the client's initial settings if the
--skip-character-set-client-handshake
option is used.
|
A.11.11. |
Why do some LIKE and
FULLTEXT searches with CJK characters fail?
|
|
For LIKE searches, there is a very
simple problem with binary string column types such as
BINARY and
BLOB: we must know where
characters end. With multibyte character sets, different
characters might have different octet lengths. For example, in
utf8, A requires one byte
but ペ requires three bytes, as shown here:
+-------------------------+---------------------------+
| OCTET_LENGTH(_utf8 'A') | OCTET_LENGTH(_utf8 'ペ') |
+-------------------------+---------------------------+
| 1 | 3 |
+-------------------------+---------------------------+
If we do not know where the first character in a string ends, we
do not know where the second character begins, in which case
even very simple searches such as
LIKE '_A%' fail.
The solution is to use a nonbinary string column type defined to
have the proper CJK character set. For example: mycol
TEXT CHARACTER SET sjis. Alternatively, convert to a
CJK character set before comparing.
This is one reason why MySQL cannot permit encodings of
nonexistent characters. If it is not strict about rejecting bad
input, it has no way of knowing where characters end.
For FULLTEXT searches, we must know where
words begin and end. With Western languages, this is rarely a
problem because most (if not all) of these use an
easy-to-identify word boundary: the space character. However,
this is not usually the case with Asian writing. We could use
arbitrary halfway measures, like assuming that all Han
characters represent words, or (for Japanese) depending on
changes from Katakana to Hiragana due to grammatical endings.
However, the only sure solution requires a comprehensive word
list, which means that we would have to include a dictionary in
the server for each Asian language supported. This is simply not
feasible.
|
A.11.12. |
How do I know whether character X is
available in all character sets?
|
|
The majority of simplified Chinese and basic nonhalfwidth
Japanese Kana characters appear in all CJK character sets. The
following stored procedure accepts a UCS-2
Unicode character, converts it to other character sets, and
displays the results in hexadecimal.
DELIMITER //
CREATE PROCEDURE p_convert(ucs2_char CHAR(1) CHARACTER SET ucs2)
BEGIN
CREATE TABLE tj
(ucs2 CHAR(1) character set ucs2,
utf8 CHAR(1) character set utf8,
big5 CHAR(1) character set big5,
cp932 CHAR(1) character set cp932,
eucjpms CHAR(1) character set eucjpms,
euckr CHAR(1) character set euckr,
gb2312 CHAR(1) character set gb2312,
gbk CHAR(1) character set gbk,
sjis CHAR(1) character set sjis,
ujis CHAR(1) character set ujis);
INSERT INTO tj (ucs2) VALUES (ucs2_char);
UPDATE tj SET utf8=ucs2,
big5=ucs2,
cp932=ucs2,
eucjpms=ucs2,
euckr=ucs2,
gb2312=ucs2,
gbk=ucs2,
sjis=ucs2,
ujis=ucs2;
/* If there are conversion problems, UPDATE produces warnings. */
SELECT hex(ucs2) AS ucs2,
hex(utf8) AS utf8,
hex(big5) AS big5,
hex(cp932) AS cp932,
hex(eucjpms) AS eucjpms,
hex(euckr) AS euckr,
hex(gb2312) AS gb2312,
hex(gbk) AS gbk,
hex(sjis) AS sjis,
hex(ujis) AS ujis
FROM tj;
DROP TABLE tj;
END//
DELIMITER ;
The input can be any single ucs2 character,
or it can be the code value (hexadecimal representation) of that
character. For example, from Unicode's list of
ucs2 encodings and names
(http://www.unicode.org/Public/UNIDATA/UnicodeData.txt),
we know that the Katakana character
Pe appears in all CJK character
sets, and that its code value is X'30DA'. If
we use this value as the argument to
p_convert(), the result is as shown here:
mysql> CALL p_convert(X'30DA');
+------+--------+------+-------+---------+-------+--------+------+------+------+
| ucs2 | utf8 | big5 | cp932 | eucjpms | euckr | gb2312 | gbk | sjis | ujis |
+------+--------+------+-------+---------+-------+--------+------+------+------+
| 30DA | E3839A | C772 | 8379 | A5DA | ABDA | A5DA | A5DA | 8379 | A5DA |
+------+--------+------+-------+---------+-------+--------+------+------+------+
Since none of the column values is 3F (that
is, the question mark character, ?), we know
that every conversion worked.
|
A.11.13. |
Why do CJK strings sort incorrectly in Unicode? (I)
|
|
CJK sorting problems that occurred in older MySQL versions can
be solved as of MySQL 8.0 by using the
utf8mb4 character set and the
utf8mb4_ja_0900_as_cs collation.
|
A.11.14. |
Why do CJK strings sort incorrectly in Unicode? (II)
|
|
CJK sorting problems that occurred in older MySQL versions can
be solved as of MySQL 8.0 by using the
utf8mb4 character set and the
utf8mb4_ja_0900_as_cs collation.
|
A.11.15. |
Why are my supplementary characters rejected by MySQL?
|
|
Supplementary characters lie outside the Unicode Basic
Multilingual Plane / Plane 0. BMP characters have
code point values between U+0000 and
U+FFFF. Supplementary characters have code
point values between U+10000 and
U+10FFFF.
To store supplementary characters, you must use a character set
that permits them:
The utf8 and ucs2
character sets support BMP characters only.
The utf8 character set permits only
UTF-8 characters that take up to three
bytes. This has led to reports such as that found in Bug
#12600, which we rejected as “not a bug”. With
utf8, MySQL must truncate an input string
when it encounters bytes that it does no understand.
Otherwise, it is unknown how long the bad multibyte
character is.
One possible workaround is to use ucs2
instead of utf8, in which case the
“bad” characters are changed to question marks.
However, no truncation takes place. You can also change the
data type to BLOB or
BINARY, which perform no
validity checking.
The utf8mb4, utf16,
utf16le, and utf32
character sets support BMP characters, as well as
supplementary characters outside the BMP.
|
A.11.16. |
Should “CJK” be “CJKV”?
|
|
No. The term “CJKV”
(Chinese Japanese Korean
Vietnamese) refers to Vietnamese character sets which
contain Han (originally Chinese) characters. MySQL supports the
modern Vietnamese script with Western characters, but does not
support the old Vietnamese script using Han characters.
As of MySQL 5.6, there are Vietnamese collations for Unicode
character sets, as described in
Section 12.10.1, “Unicode Character Sets”.
|
A.11.17. |
Does MySQL permit CJK characters to be used in database and
table names?
|
|
Yes.
|
A.11.18. |
Where can I find translations of the MySQL Manual into Chinese,
Japanese, and Korean?
|
|
The Japanese translation of the MySQL 5.6 manual can be
downloaded from https://dev.mysql.com/doc/.
|
A.11.19. |
Where can I get help with CJK and related issues in MySQL?
|
|
The following resources are available:
|