【trouble-shooting】MySQL中文乱码，如何设置utf8
问题情境
create table score (
student_id int,
subject varchar(10),
subject_score int
);
insert into score values (001,'数学',50),(002,'数学',60),(003,'数学',70);
”数学“中文字符不能顺利显示
解决问题
中文乱码，是因为MySQL现在的 ”Character Set 字符集合“ 只能识别英文字符和数字字符，不能识别”中文字符“所导致的
到底什么叫Character Set呢？
打个比方，现在有一篇文章
我不想看文字了，我想听有声书，这时候我就需要下载语音包，我想听粤语，我就使用”粤语语音包“，想听”东北话“，就使用”东北话语音包“
“character set 字符集合” 跟”语音包“ 很类似，只不过前者是”看“的，后者是”听“的
Character Set 里面到底有什么呢？
1.符号 symbols
2.编码 encoding
#查询数据库使用的字符集
mysql> SELECT @@character_set_database;
+--------------------------+
| @@character_set_database |
+--------------------------+
| latin1 |
+--------------------------+
1 row in set (0.00 sec)
刚才的中文乱码，就是因为正在使用的"latin1 character set"并不包含”中文符号“，所以我们需要换一个包含”中文符号“的character set，如utf8
character set有4个维度
1.列的 character set
2.表的 character set
3.数据库的 character set
4.服务器的 character set
它们之间的关系是包含于被包含
服务器的character set 需要在启动的时候修改，现在可以考虑在database层面修改
#查询可以选择的character set
mysql> show character set;
+----------+-----------------------------+---------------------+--------+
| 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 |
| utf8mb4 | UTF-8 Unicode | utf8mb4_general_ci | 4 |
| cp1251 | Windows Cyrillic | cp1251_general_ci | 1 |
| utf16 | UTF-16 Unicode | utf16_general_ci | 4 |
| cp1256 | Windows Arabic | cp1256_general_ci | 1 |
| cp1257 | Windows Baltic | cp1257_general_ci | 1 |
| utf32 | UTF-32 Unicode | utf32_general_ci | 4 |
| 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 |
+----------+-----------------------------+---------------------+--------+
39 rows in set (0.00 sec)
#修改数据库编码
alter database character set utf8
#确认一下
SELECT @@character_set_database;
+--------------------------+
| @@character_set_database |
+--------------------------+
| utf8 |
+--------------------------+
1 row in set (0.00 sec)
再次查询，还是未能看到”中文“，那是因为table是按照latin1 character set 创建的，只有重新创建的table才会有新的utf8 character set
#查询表格的character set
mysql> show create table score;
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| score | CREATE TABLE `score` (
`student_id` int(11) DEFAULT NULL,
`subject` varchar(10) DEFAULT NULL,
`subject_score` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
#修改表格的character set
mysql> alter table score character set utf8;
Query OK, 3 rows affected (0.01 sec)
Records: 3 Duplicates: 0 Warnings: 0
还是不能正常显示中文字符，这时因为”column字段“，还是按照原来默认的方式创建了，column是最低的维度
mysql> show create table score;
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| score | CREATE TABLE `score` (
`student_id` int(11) DEFAULT NULL,
`subject` varchar(10) CHARACTER SET latin1 DEFAULT NULL,
`subject_score` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
所以还需要把列的character set修改一下
mysql> alter table score modify subject varchar(10) character set utf8; Query OK, 3 rows affected (0.04 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql> select * from score; +------------+---------+---------------+ | student_id | subject | subject_score | +------------+---------+---------------+ | 1 | ?? | 50 | | 2 | ?? | 60 | | 3 | ?? | 70 | +------------+---------+---------------+ 3 rows in set (0.00 sec) mysql> show create table score; +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table | +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | score | CREATE TABLE `score` ( `student_id` int(11) DEFAULT NULL, `subject` varchar(10) DEFAULT NULL, `subject_score` int(11) DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=utf8 | +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec)
继续检查
mysql> SHOW VARIABLES LIKE 'character_set%';
+--------------------------+---------------------------------------------------------+
| Variable_name | Value |
+--------------------------+---------------------------------------------------------+
| character_set_client | utf8 |
| character_set_connection | utf8 |
| character_set_database | utf8 |
| character_set_filesystem | binary |
| character_set_results | utf8 |
| character_set_server | latin1 |
| character_set_system | utf8 |
| character_sets_dir | /usr/local/mysql-5.5.47-linux2.6-x86_64/share/charsets/ |
+--------------------------+---------------------------------------------------------+
8 rows in set (0.00 sec)
mysql> set character_set_server=utf8;
Query OK, 0 rows affected (0.00 sec)
mysql> insert into score values (001,'数学',50),(002,'数学',60),(003,'数学',70); Query OK, 3 rows affected (0.00 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql> select * from score; +------------+---------+---------------+ | student_id | subject | subject_score | +------------+---------+---------------+ | 1 | ?? | 50 | | 2 | ?? | 60 | | 3 | ?? | 70 | | 1 | 数学 | 50 | | 2 | 数学 | 60 | | 3 | 数学 | 70 | +------------+---------+-------
还是不能解决乱码问题，后来在stackoverflow提了这个问题：How to solve Chinese character display in MySQL?
才发现原来，修改字符集，只能对新的数据起作用，旧的数据不会影响的 how to save my old records? - they already damaged on insert, multibyte content was thrown away and just saved as ?
