mysql 配置与中文乱码解决方案

一、关于数据库引擎及配置问题

mysql 支持多种数据引擎，针对不同的数据库引擎引擎应用，应当进行相应的配置，对于初学者，最简单的方法莫过于，从/usr/share/mysql下，拷贝相应的配置到/etc/my.cnf。/usr/share/mysql下有以下配置文件：my-huge.cnf，my-innodb-heavy-4g.cnf，my-large.cnf，my-medium.cnf，my-small.cnf，直接将对应的配置文件复制到/etc/下，改名为my.cnf即可。

二、Mysql无法建InnoDB表的问题

笔者在按照以上方法改变了MYSQL配置后，发现无法创建INNODB数据引擎的数据表，原因在：http://blog.csdn.net/yufangbo/archive/2009/05/14/4182007.aspx 中有叙述，主要是，关闭MYSQL，然后找到/var/lib/mysql目录下ibdataN和ib_logfileN文件，不管多少个，都删掉，然后，重启mysql即可。

三、charset问题

由于涉及到中文，数据存储存在显示乱码，存储超线问题，比如，varchar(20)字段，到底是存储20个中文还是6个中文或者10中文？在mssql中，中文已经和英文一样对待了，所以，我们的意图应该是存储20个中文。

同样，我们在对字符运算过程中也存在问题，比如length，substring等函数，如果中文是分几个字节存储，如果我们substring后，发现是乱码怎么办？这完全有可能。

笔者尝试了多种方法，最后发现全部采用utf8是最佳方案，具体做法如下：

1、配置mysql

打开my.cnf以后，在[client]和[mysqld]下面均加上default-character-set=utf8，保存并关闭，重启mysql。

2、查看mysql内码设置

查看 MySQL 数据库服务器和数据库字符集。

mysql> show variables like '%char%';
+--------------------------+-------------------------------------+------
| Variable_name            | Value                               |......
+--------------------------+-------------------------------------+------
| character_set_client     | utf8                                |......   -- 客户端字符集
| character_set_connection | utf8                                |......
| character_set_database   | utf8                                |......   -- 数据库字符集
| character_set_filesystem | binary                              |......
| character_set_results    | utf8                                |......
| character_set_server     | utf8                                |......   -- 服务器字符集
| character_set_system     | utf8                                |......
| character_sets_dir       | D:/MySQL Server 5.0/share/charsets/ |......
+--------------------------+-------------------------------------+------

查看 MySQL 数据表（table） 的字符集。

mysql> show table status from sqlstudy_db like '%countries%';
+-----------+--------+---------+------------+------+-----------------+------
| Name      | Engine | Version | Row_format | Rows | Collation       |......
+-----------+--------+---------+------------+------+-----------------+------
| countries | InnoDB |      10 | Compact    |   11 | utf8_general_ci |......
+-----------+--------+---------+------------+------+-----------------+------

查看 MySQL 数据列（column）的字符集。

mysql> show full columns from countries;
+----------------------+-------------+-----------------+--------
| Field                | Type        | Collation       | .......
+----------------------+-------------+-----------------+--------
| countries_id         | int(11)     | NULL            | .......
| countries_name       | varchar(64) | utf8_general_ci | .......
| countries_iso_code_2 | char(2)     | utf8_general_ci | .......
| countries_iso_code_3 | char(3)     | utf8_general_ci | .......
| address_format_id    | int(11)     | NULL            | .......
+----------------------+-------------+-----------------+--------

查看当前安装的 MySQL 所支持的字符集。

mysql> show charset;
+----------+-----------------------------+---------------------+--------+
| Charset  | Description                 | Default collation   | Maxlen |
+----------+-----------------------------+---------------------+--------+
| big5     | Big5 Traditional Chinese    | big5_chinese_ci     |      2 |
| dec8     | DEC West European           | dec8_swedish_ci     |      1 |
| cp850    | DOS West European           | cp850_general_ci    |      1 |
| hp8      | HP West European            | hp8_english_ci      |      1 |
| koi8r    | KOI8-R Relcom Russian       | koi8r_general_ci    |      1 |
| latin1   | cp1252 West European        | latin1_swedish_ci   |      1 |
| latin2   | ISO 8859-2 Central European | latin2_general_ci   |      1 |
| swe7     | 7bit Swedish                | swe7_swedish_ci     |      1 |
| ascii    | US ASCII                    | ascii_general_ci    |      1 |
| ujis     | EUC-JP Japanese             | ujis_japanese_ci    |      3 |
| sjis     | Shift-JIS Japanese          | sjis_japanese_ci    |      2 |
| hebrew   | ISO 8859-8 Hebrew           | hebrew_general_ci   |      1 |
| tis620   | TIS620 Thai                 | tis620_thai_ci      |      1 |
| euckr    | EUC-KR Korean               | euckr_korean_ci     |      2 |
| koi8u    | KOI8-U Ukrainian            | koi8u_general_ci    |      1 |
| gb2312   | GB2312 Simplified Chinese   | gb2312_chinese_ci   |      2 |
| greek    | ISO 8859-7 Greek            | greek_general_ci    |      1 |
| cp1250   | Windows Central European    | cp1250_general_ci   |      1 |
| gbk      | GBK Simplified Chinese      | gbk_chinese_ci      |      2 |
| latin5   | ISO 8859-9 Turkish          | latin5_turkish_ci   |      1 |
| armscii8 | ARMSCII-8 Armenian          | armscii8_general_ci |      1 |
| utf8     | UTF-8 Unicode               | utf8_general_ci     |      3 |
| ucs2     | UCS-2 Unicode               | ucs2_general_ci     |      2 |
| cp866    | DOS Russian                 | cp866_general_ci    |      1 |
| keybcs2  | DOS Kamenicky Czech-Slovak  | keybcs2_general_ci  |      1 |
| macce    | Mac Central European        | macce_general_ci    |      1 |
| macroman | Mac West European           | macroman_general_ci |      1 |
| cp852    | DOS Central European        | cp852_general_ci    |      1 |
| latin7   | ISO 8859-13 Baltic          | latin7_general_ci   |      1 |
| cp1251   | Windows Cyrillic            | cp1251_general_ci   |      1 |
| cp1256   | Windows Arabic              | cp1256_general_ci   |      1 |
| cp1257   | Windows Baltic              | cp1257_general_ci   |      1 |
| binary   | Binary pseudo charset       | binary              |      1 |
| geostd8  | GEOSTD8 Georgian            | geostd8_general_ci  |      1 |
| cp932    | SJIS for Windows Japanese   | cp932_japanese_ci   |      2 |
| eucjpms  | UJIS for Windows Japanese   | eucjpms_japanese_ci |      3 |

+----------+-----------------------------+---------------------+--------+
查看mysql字符集是为了我们确认当前使用了什么字符集。

3、创建数据库和数据表，习惯性加上charset选项

create database sample default  charset=utf8;

对已有的数据库进行修改：
ALTER DATABASE sample
CHARACTER SET utf8
DEFAULT CHARACTER SET utf8
COLLATE utf8_general_ci
DEFAULT COLLATE utf8_general_ci;

create table tbluser (
user_id varchar(20) primary key,
user_name varchar(20) not null,
user_pwd varchar(20) not null,
user_birthday date not null,
user_sex char(1) not null,
user_email varchar(50) not null,
user_role char(1) not null,
user_status char(1) not null
)default charset=utf8;

4、统计字符串长度，使用char_length
length:   是计算字段的长度一个汉字是算三个字符,一个数字或字母算一个字符
char_length:不管汉字还是数字或者是字母都算是一个字符

采用以上办法，彻底解决了中文字符乱码和中文字符运算问题。