关于mysql在linux下面字符修改的问题

You inserted CJK characters with

INSERT

, but when you do a

SELECT

, they all look like “?”. It usually is a setting in MySQL that doesn't match the settings for the application program or the operating system. These are common troubleshooting steps:

Find out: what version do you have? The statement

SELECT VERSION();

will tell you. This FAQ is for MySQL version 5, so some of the answers here will not apply to you if you have version 4.0 or 4.1.

Find out: what character set is the database column really in? Too frequently, people think that the character set will be the same as the server's set (false), or the set used for display purposes (false). Make sure, by saying

SHOW CREATE TABLE tablename

, or better yet by saying this:

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;

Find out: what is the hexadecimal value?

SELECT HEX(your_column_name)
FROM your_table_name;

If you see

3F

, then that really is the encoding for

?

, so no wonder you see “?”. Probably this happened because of a problem converting a particular character from your client character set to the target character set.

Find out: is a literal round trip possible, that is, if you select “literal” (or “_introducer hexadecimal-value”) do you get “literal” as a result? For example, with the Japanese Katakana Letter Pe, which looks like

ペ'

, and which exists in all CJK character sets, and which has the code point value (hexadecimal coding)

0x30da

, enter:

SELECT 'ペ' AS `ペ`;         /* or SELECT _ucs2 0x30da; */

If the result doesn't look like

ペ

, a round trip failed. For bug reports, we might ask people to follow up with

SELECT hex('ペ');

. Then we can see whether the client encoding is right.

Find out: is it the browser or application? Just use mysql (the MySQL client program, which on Windows will be mysql.exe). If mysql displays correctly but your application doesn't, then your problem is probably “Settings”, but consult also the question about “Troubles with Access (or Perl) (or PHP) (etc.)” much later in this FAQ.

To find your settings, the statement you need here is

SHOW VARIABLES

. For example:

mysql> [code]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/ |
+--------------------------+----------------------------------------+
8 rows in set (0.03 sec)
[/code]
The above 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 and a default for MySQL).

Although Unicode (usually the

utf8

variant on Unix, usually the

ucs2

variant on Windows) is better than “latin”, it's 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 what's suitable.

If you can't control the server settings, and you have no idea what your underlying computer is about, then try changing to a common character set for the country that you're in (

euckr

= Korea,

gb2312

or

gbk

= People's Republic of China,

big5

= other China,

sjis

or

ujis

or

cp932

or

eucjpms

= Japan,

ucs2

or

utf8

= anywhere). Usually it is only necessary to change the client and connection and results settings, and there is a simple statement which changes all three at once, namely

SET NAMES

. For example:

SET NAMES 'big5';

Once you get the correct setting, you can make it permanent by editing

my.cnf

or

my.ini

. For example you might add lines looking like this:

[mysqld]
character-set-server=big5
[client]
default-character-set=big5