MySQL(二十)-字符集和比较规则
参考文献
- 高性能MySQL(第三版)
- MySQL是怎样运行的
字符集和比较规则
- 字符集是指一种二进制编码到某类字符符号的映射.
- 比较规则是指一组用于某个字符集的排序规则.
- MySQL有很多的选项用于控制字符集.这些选项和字符集很容易混淆,一定要记住:只有基于字符的值才真正的"有"字符集的概念.对于其他类型的值,字符集只是一个设置,指定用哪一种字符集来做比较或者其他操作.基于字符的值能存放在某列中,查询的字符串中,表达式的计算结果中或者某个用户变量中,等等.
- MySQL的设置可以分为两类:
- 创建对象时的默认值;
- 在服务器和客户端通信时的设置;
一些重要的字符集
ASCII字符集:共收录128个字符集,包括空格,标点符号,数字,大小写字母和一些不可见字符.ISO 8859-1字符集: 共收录256个字符,它在ASCII字符集的基础上又扩充了128个西欧常用字符.ISO 8859-1字符集也可以使用一个字节来进行编码(这个字符集也有一个别名Latin1)GB2312字符集: 这个字符集同时又兼容ASCII字符集,所以在编码方式上显得有些奇怪: 如果该字符在ASCII字符集中,则采用一字节编码;否则采用两字节编码.GBK字符集UTF-8字符集MySQL并不区分字符集和编码
创建对象时的默认设置
-
MySQL服务器有默认的字符集和比较规则规则,每个数据库也有自己的默认值,每个表也有自己的默认值.这是一个逐层继承的默认设置,最终最靠底层的默认设置将影响创建的对象.-
创建数据库的时候,将根据服务器上的
character_set_server设置来设定该数据库的默认字符集. -
创建表的时候,将根据数据库的字符集设置指定这个表的字符集设置.
-
创建列的时候,将根据表的设置指定列的字符集设置.
-
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需要注意的是,真正存放数据的列,所以更高阶梯的设置只是指定默认值.一个表的默认字符集设置无法影响存储在这个表中某个列的值.只有当创建列而没有为列指定字符集的时候,如果没有指定字符集,表的默认字符集才能起作用.
服务器和客户端通信时的设置
- 当服务器和客户端通信时候,它们可能使用不同的字符集.这时,服务器端将进行必要的翻译转换工作:
- 服务器端总是假设客户端是按照
character_set_clinet设置的字符来传输数据和SQL语句的. - 当服务器收到客户端的SQL语句时,它先将其转换成字符集
character_set_connection.它还使用这个设置来决定如何将数据转换成字符串. - 当服务器端返回数据或者错误信息给客户端时,它会将其转换成
character_set_results;
- 服务器端总是假设客户端是按照
一些特殊情况
诡异的character_set_database设置
character_set_database设置的默认值和默认数据库的设置相同.当改变默认数据库字符集的时候,这个变量也会跟着变.所以当连接到MySQL实例上又没有指定要使用的数据库字符集,默认值会和character_set_server相同.
LOAD DATA INFILE
- 当使用
LOAD DATA INFILE的时候,数据库总是将恩建中字符按照字符集character_set_database来解析.在MySQL5.0和更新的版本中,可以在LOAD DATA INFILE中使用子句CHARACTER SET来设定字符集,不过最好不要依赖这个设定.最好的方式是先使用USE指定数据库,在执行SET NAMES来设定字符集,最后在加载数据. MySQL在加载数据的时候,总是以同样的字符集处理所有数据,而不管表中的列是否有不同的字符集设定.
SELECT INTO OUTFILE
MySQL会将SELECT INTO OUTFILE的结果不做任何转码的写入文件.
查看和设置字符集
-
当在排序或者比较过程中遇到问题时,应当检查字符集选项与表的定义.
-
显示字符集变量值
1
2SHOW VARIABLES LIKE 'character_set_%'; -- 查看所有字符集编码项
SHOW VARIABLES LIKE '%%coll%';character_set_client: 客户端向服务器发送数据时使用的编码character_set_results: 服务器端将结果返回给客户端所使用的编码character_set_connection: 连接层编码
-
设置字符集集
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5SET 变量名 = 变量值
SET character_set_client = gbk;
SET character_set_results = gbk;
SET character_set_connection = gbk;
SET NAMES GBK; -- 相当于完成以上三个设置 -
比较规则
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5-- 比较规则用以排序
SHOW (CHARACTER SET |CHARSET) [LIKE 'pattern'] 查看所有字符集
SHOW COLLATION [LIKE 'pattern'] 查看所有比较规则
# CHARSET 字符集编码 设置字符集编码
# COLLATE 比较规则编码 设置比较规则编码1
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47mysql> show charset;
+----------+---------------------------------+---------------------+--------+
| Charset | Description | Default collation | Maxlen |
+----------+---------------------------------+---------------------+--------+
| armscii8 | ARMSCII-8 Armenian | armscii8_general_ci | 1 |
| ascii | US ASCII | ascii_general_ci | 1 |
| big5 | Big5 Traditional Chinese | big5_chinese_ci | 2 |
| binary | Binary pseudo charset | binary | 1 |
| cp1250 | Windows Central European | cp1250_general_ci | 1 |
| cp1251 | Windows Cyrillic | cp1251_general_ci | 1 |
| cp1256 | Windows Arabic | cp1256_general_ci | 1 |
| cp1257 | Windows Baltic | cp1257_general_ci | 1 |
| cp850 | DOS West European | cp850_general_ci | 1 |
| cp852 | DOS Central European | cp852_general_ci | 1 |
| cp866 | DOS Russian | cp866_general_ci | 1 |
| cp932 | SJIS for Windows Japanese | cp932_japanese_ci | 2 |
| dec8 | DEC West European | dec8_swedish_ci | 1 |
| eucjpms | UJIS for Windows Japanese | eucjpms_japanese_ci | 3 |
| euckr | EUC-KR Korean | euckr_korean_ci | 2 |
| gb18030 | China National Standard GB18030 | gb18030_chinese_ci | 4 |
| gb2312 | GB2312 Simplified Chinese | gb2312_chinese_ci | 2 |
| gbk | GBK Simplified Chinese | gbk_chinese_ci | 2 |
| geostd8 | GEOSTD8 Georgian | geostd8_general_ci | 1 |
| greek | ISO 8859-7 Greek | greek_general_ci | 1 |
| hebrew | ISO 8859-8 Hebrew | hebrew_general_ci | 1 |
| hp8 | HP West European | hp8_english_ci | 1 |
| keybcs2 | DOS Kamenicky Czech-Slovak | keybcs2_general_ci | 1 |
| koi8r | KOI8-R Relcom Russian | koi8r_general_ci | 1 |
| koi8u | KOI8-U Ukrainian | koi8u_general_ci | 1 |
| latin1 | cp1252 West European | latin1_swedish_ci | 1 |
| latin2 | ISO 8859-2 Central European | latin2_general_ci | 1 |
| latin5 | ISO 8859-9 Turkish | latin5_turkish_ci | 1 |
| latin7 | ISO 8859-13 Baltic | latin7_general_ci | 1 |
| macce | Mac Central European | macce_general_ci | 1 |
| macroman | Mac West European | macroman_general_ci | 1 |
| sjis | Shift-JIS Japanese | sjis_japanese_ci | 2 |
| swe7 | 7bit Swedish | swe7_swedish_ci | 1 |
| tis620 | TIS620 Thai | tis620_thai_ci | 1 |
| ucs2 | UCS-2 Unicode | ucs2_general_ci | 2 |
| ujis | EUC-JP Japanese | ujis_japanese_ci | 3 |
| utf16 | UTF-16 Unicode | utf16_general_ci | 4 |
| utf16le | UTF-16LE Unicode | utf16le_general_ci | 4 |
| utf32 | UTF-32 Unicode | utf32_general_ci | 4 |
| utf8mb3 | UTF-8 Unicode | utf8mb3_general_ci | 3 |
| utf8mb4 | UTF-8 Unicode | utf8mb4_0900_ai_ci | 4 |
+----------+---------------------------------+---------------------+--------+
41 rows in set (0.04 sec)1
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123mysql> SHOW COLLATION LIKE 'utf8_%';
+-----------------------------+---------+-----+---------+----------+---------+---------------+
| Collation | Charset | Id | Default | Compiled | Sortlen | Pad_attribute |
+-----------------------------+---------+-----+---------+----------+---------+---------------+
| utf8mb3_bin | utf8mb3 | 83 | | Yes | 1 | PAD SPACE |
| utf8mb3_croatian_ci | utf8mb3 | 213 | | Yes | 8 | PAD SPACE |
| utf8mb3_czech_ci | utf8mb3 | 202 | | Yes | 8 | PAD SPACE |
| utf8mb3_danish_ci | utf8mb3 | 203 | | Yes | 8 | PAD SPACE |
| utf8mb3_esperanto_ci | utf8mb3 | 209 | | Yes | 8 | PAD SPACE |
| utf8mb3_estonian_ci | utf8mb3 | 198 | | Yes | 8 | PAD SPACE |
| utf8mb3_general_ci | utf8mb3 | 33 | Yes | Yes | 1 | PAD SPACE |
| utf8mb3_general_mysql500_ci | utf8mb3 | 223 | | Yes | 1 | PAD SPACE |
| utf8mb3_german2_ci | utf8mb3 | 212 | | Yes | 8 | PAD SPACE |
| utf8mb3_hungarian_ci | utf8mb3 | 210 | | Yes | 8 | PAD SPACE |
| utf8mb3_icelandic_ci | utf8mb3 | 193 | | Yes | 8 | PAD SPACE |
| utf8mb3_latvian_ci | utf8mb3 | 194 | | Yes | 8 | PAD SPACE |
| utf8mb3_lithuanian_ci | utf8mb3 | 204 | | Yes | 8 | PAD SPACE |
| utf8mb3_persian_ci | utf8mb3 | 208 | | Yes | 8 | PAD SPACE |
| utf8mb3_polish_ci | utf8mb3 | 197 | | Yes | 8 | PAD SPACE |
| utf8mb3_romanian_ci | utf8mb3 | 195 | | Yes | 8 | PAD SPACE |
| utf8mb3_roman_ci | utf8mb3 | 207 | | Yes | 8 | PAD SPACE |
| utf8mb3_sinhala_ci | utf8mb3 | 211 | | Yes | 8 | PAD SPACE |
| utf8mb3_slovak_ci | utf8mb3 | 205 | | Yes | 8 | PAD SPACE |
| utf8mb3_slovenian_ci | utf8mb3 | 196 | | Yes | 8 | PAD SPACE |
| utf8mb3_spanish2_ci | utf8mb3 | 206 | | Yes | 8 | PAD SPACE |
| utf8mb3_spanish_ci | utf8mb3 | 199 | | Yes | 8 | PAD SPACE |
| utf8mb3_swedish_ci | utf8mb3 | 200 | | Yes | 8 | PAD SPACE |
| utf8mb3_tolower_ci | utf8mb3 | 76 | | Yes | 1 | PAD SPACE |
| utf8mb3_turkish_ci | utf8mb3 | 201 | | Yes | 8 | PAD SPACE |
| utf8mb3_unicode_520_ci | utf8mb3 | 214 | | Yes | 8 | PAD SPACE |
| utf8mb3_unicode_ci | utf8mb3 | 192 | | Yes | 8 | PAD SPACE |
| utf8mb3_vietnamese_ci | utf8mb3 | 215 | | Yes | 8 | PAD SPACE |
| utf8mb4_0900_ai_ci | utf8mb4 | 255 | Yes | Yes | 0 | NO PAD |
| utf8mb4_0900_as_ci | utf8mb4 | 305 | | Yes | 0 | NO PAD |
| utf8mb4_0900_as_cs | utf8mb4 | 278 | | Yes | 0 | NO PAD |
| utf8mb4_0900_bin | utf8mb4 | 309 | | Yes | 1 | NO PAD |
| utf8mb4_bg_0900_ai_ci | utf8mb4 | 318 | | Yes | 0 | NO PAD |
| utf8mb4_bg_0900_as_cs | utf8mb4 | 319 | | Yes | 0 | NO PAD |
| utf8mb4_bin | utf8mb4 | 46 | | Yes | 1 | PAD SPACE |
| utf8mb4_bs_0900_ai_ci | utf8mb4 | 316 | | Yes | 0 | NO PAD |
| utf8mb4_bs_0900_as_cs | utf8mb4 | 317 | | Yes | 0 | NO PAD |
| utf8mb4_croatian_ci | utf8mb4 | 245 | | Yes | 8 | PAD SPACE |
| utf8mb4_cs_0900_ai_ci | utf8mb4 | 266 | | Yes | 0 | NO PAD |
| utf8mb4_cs_0900_as_cs | utf8mb4 | 289 | | Yes | 0 | NO PAD |
| utf8mb4_czech_ci | utf8mb4 | 234 | | Yes | 8 | PAD SPACE |
| utf8mb4_danish_ci | utf8mb4 | 235 | | Yes | 8 | PAD SPACE |
| utf8mb4_da_0900_ai_ci | utf8mb4 | 267 | | Yes | 0 | NO PAD |
| utf8mb4_da_0900_as_cs | utf8mb4 | 290 | | Yes | 0 | NO PAD |
| utf8mb4_de_pb_0900_ai_ci | utf8mb4 | 256 | | Yes | 0 | NO PAD |
| utf8mb4_de_pb_0900_as_cs | utf8mb4 | 279 | | Yes | 0 | NO PAD |
| utf8mb4_eo_0900_ai_ci | utf8mb4 | 273 | | Yes | 0 | NO PAD |
| utf8mb4_eo_0900_as_cs | utf8mb4 | 296 | | Yes | 0 | NO PAD |
| utf8mb4_esperanto_ci | utf8mb4 | 241 | | Yes | 8 | PAD SPACE |
| utf8mb4_estonian_ci | utf8mb4 | 230 | | Yes | 8 | PAD SPACE |
| utf8mb4_es_0900_ai_ci | utf8mb4 | 263 | | Yes | 0 | NO PAD |
| utf8mb4_es_0900_as_cs | utf8mb4 | 286 | | Yes | 0 | NO PAD |
| utf8mb4_es_trad_0900_ai_ci | utf8mb4 | 270 | | Yes | 0 | NO PAD |
| utf8mb4_es_trad_0900_as_cs | utf8mb4 | 293 | | Yes | 0 | NO PAD |
| utf8mb4_et_0900_ai_ci | utf8mb4 | 262 | | Yes | 0 | NO PAD |
| utf8mb4_et_0900_as_cs | utf8mb4 | 285 | | Yes | 0 | NO PAD |
| utf8mb4_general_ci | utf8mb4 | 45 | | Yes | 1 | PAD SPACE |
| utf8mb4_german2_ci | utf8mb4 | 244 | | Yes | 8 | PAD SPACE |
| utf8mb4_gl_0900_ai_ci | utf8mb4 | 320 | | Yes | 0 | NO PAD |
| utf8mb4_gl_0900_as_cs | utf8mb4 | 321 | | Yes | 0 | NO PAD |
| utf8mb4_hr_0900_ai_ci | utf8mb4 | 275 | | Yes | 0 | NO PAD |
| utf8mb4_hr_0900_as_cs | utf8mb4 | 298 | | Yes | 0 | NO PAD |
| utf8mb4_hungarian_ci | utf8mb4 | 242 | | Yes | 8 | PAD SPACE |
| utf8mb4_hu_0900_ai_ci | utf8mb4 | 274 | | Yes | 0 | NO PAD |
| utf8mb4_hu_0900_as_cs | utf8mb4 | 297 | | Yes | 0 | NO PAD |
| utf8mb4_icelandic_ci | utf8mb4 | 225 | | Yes | 8 | PAD SPACE |
| utf8mb4_is_0900_ai_ci | utf8mb4 | 257 | | Yes | 0 | NO PAD |
| utf8mb4_is_0900_as_cs | utf8mb4 | 280 | | Yes | 0 | NO PAD |
| utf8mb4_ja_0900_as_cs | utf8mb4 | 303 | | Yes | 0 | NO PAD |
| utf8mb4_ja_0900_as_cs_ks | utf8mb4 | 304 | | Yes | 24 | NO PAD |
| utf8mb4_latvian_ci | utf8mb4 | 226 | | Yes | 8 | PAD SPACE |
| utf8mb4_la_0900_ai_ci | utf8mb4 | 271 | | Yes | 0 | NO PAD |
| utf8mb4_la_0900_as_cs | utf8mb4 | 294 | | Yes | 0 | NO PAD |
| utf8mb4_lithuanian_ci | utf8mb4 | 236 | | Yes | 8 | PAD SPACE |
| utf8mb4_lt_0900_ai_ci | utf8mb4 | 268 | | Yes | 0 | NO PAD |
| utf8mb4_lt_0900_as_cs | utf8mb4 | 291 | | Yes | 0 | NO PAD |
| utf8mb4_lv_0900_ai_ci | utf8mb4 | 258 | | Yes | 0 | NO PAD |
| utf8mb4_lv_0900_as_cs | utf8mb4 | 281 | | Yes | 0 | NO PAD |
| utf8mb4_mn_cyrl_0900_ai_ci | utf8mb4 | 322 | | Yes | 0 | NO PAD |
| utf8mb4_mn_cyrl_0900_as_cs | utf8mb4 | 323 | | Yes | 0 | NO PAD |
| utf8mb4_nb_0900_ai_ci | utf8mb4 | 310 | | Yes | 0 | NO PAD |
| utf8mb4_nb_0900_as_cs | utf8mb4 | 311 | | Yes | 0 | NO PAD |
| utf8mb4_nn_0900_ai_ci | utf8mb4 | 312 | | Yes | 0 | NO PAD |
| utf8mb4_nn_0900_as_cs | utf8mb4 | 313 | | Yes | 0 | NO PAD |
| utf8mb4_persian_ci | utf8mb4 | 240 | | Yes | 8 | PAD SPACE |
| utf8mb4_pl_0900_ai_ci | utf8mb4 | 261 | | Yes | 0 | NO PAD |
| utf8mb4_pl_0900_as_cs | utf8mb4 | 284 | | Yes | 0 | NO PAD |
| utf8mb4_polish_ci | utf8mb4 | 229 | | Yes | 8 | PAD SPACE |
| utf8mb4_romanian_ci | utf8mb4 | 227 | | Yes | 8 | PAD SPACE |
| utf8mb4_roman_ci | utf8mb4 | 239 | | Yes | 8 | PAD SPACE |
| utf8mb4_ro_0900_ai_ci | utf8mb4 | 259 | | Yes | 0 | NO PAD |
| utf8mb4_ro_0900_as_cs | utf8mb4 | 282 | | Yes | 0 | NO PAD |
| utf8mb4_ru_0900_ai_ci | utf8mb4 | 306 | | Yes | 0 | NO PAD |
| utf8mb4_ru_0900_as_cs | utf8mb4 | 307 | | Yes | 0 | NO PAD |
| utf8mb4_sinhala_ci | utf8mb4 | 243 | | Yes | 8 | PAD SPACE |
| utf8mb4_sk_0900_ai_ci | utf8mb4 | 269 | | Yes | 0 | NO PAD |
| utf8mb4_sk_0900_as_cs | utf8mb4 | 292 | | Yes | 0 | NO PAD |
| utf8mb4_slovak_ci | utf8mb4 | 237 | | Yes | 8 | PAD SPACE |
| utf8mb4_slovenian_ci | utf8mb4 | 228 | | Yes | 8 | PAD SPACE |
| utf8mb4_sl_0900_ai_ci | utf8mb4 | 260 | | Yes | 0 | NO PAD |
| utf8mb4_sl_0900_as_cs | utf8mb4 | 283 | | Yes | 0 | NO PAD |
| utf8mb4_spanish2_ci | utf8mb4 | 238 | | Yes | 8 | PAD SPACE |
| utf8mb4_spanish_ci | utf8mb4 | 231 | | Yes | 8 | PAD SPACE |
| utf8mb4_sr_latn_0900_ai_ci | utf8mb4 | 314 | | Yes | 0 | NO PAD |
| utf8mb4_sr_latn_0900_as_cs | utf8mb4 | 315 | | Yes | 0 | NO PAD |
| utf8mb4_sv_0900_ai_ci | utf8mb4 | 264 | | Yes | 0 | NO PAD |
| utf8mb4_sv_0900_as_cs | utf8mb4 | 287 | | Yes | 0 | NO PAD |
| utf8mb4_swedish_ci | utf8mb4 | 232 | | Yes | 8 | PAD SPACE |
| utf8mb4_tr_0900_ai_ci | utf8mb4 | 265 | | Yes | 0 | NO PAD |
| utf8mb4_tr_0900_as_cs | utf8mb4 | 288 | | Yes | 0 | NO PAD |
| utf8mb4_turkish_ci | utf8mb4 | 233 | | Yes | 8 | PAD SPACE |
| utf8mb4_unicode_520_ci | utf8mb4 | 246 | | Yes | 8 | PAD SPACE |
| utf8mb4_unicode_ci | utf8mb4 | 224 | | Yes | 8 | PAD SPACE |
| utf8mb4_vietnamese_ci | utf8mb4 | 247 | | Yes | 8 | PAD SPACE |
| utf8mb4_vi_0900_ai_ci | utf8mb4 | 277 | | Yes | 0 | NO PAD |
| utf8mb4_vi_0900_as_cs | utf8mb4 | 300 | | Yes | 0 | NO PAD |
| utf8mb4_zh_0900_as_cs | utf8mb4 | 308 | | Yes | 0 | NO PAD |
+-----------------------------+---------+-----+---------+----------+---------+---------------+
117 rows in set (0.00 sec)- 比较规则名称后缀英文释义及描述
后缀 英文释义 描述 _aiaccent insensitive不区分重音 _asaccent sensitive区分重音 _cicase insensitive不区分大小写 _cscase sensitive区分大小写 _binbinary以二进制方式比较
各个级别的字符集和比较规则
服务器级别
| 系统变量 | 描述 |
|---|---|
character_set_server |
服务器级别的字符集 |
collation_server |
服务器级别的比较规则 |
数据库级别
1 | CREATE DATABASE 数据库名 |
| 系统变量 | 描述 |
|---|---|
character_set_database |
数据库级别的字符集 |
collation_database |
数据库级别的比较规则 |
表级别
1 | CREATE TABLE 表名(列的信息) |
列级别
1 | CREATE TABLE 表名( |
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