本節主要介紹查看字符集和校對規則的幾種方法。

在 MySQL 中，查看可用字符集的命令和執行過程如下：

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 | | utf16le | UTF-16LE Unicode | utf16le_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 | | gb18030 | China National Standard GB18030 | gb18030_chinese_ci | 4 | +----------+---------------------------------+---------------------+--------+ 41 rows in set (0.02 sec)

其中：

• 第一列（Charset）為字符集名稱；
• 第二列（Description）為字符集描述；
• 第三列（Default collation）為字符集的默認校對規則；
• 第四列（Maxlen）表示字符集中一個字符占用的最大字節數。

常用的字符集如下：

• latin1 支持西歐字符、希臘字符等。
• gbk 支持中文簡體字符。
• big5 支持中文繁體字符。
• utf8 幾乎支持所有國家的字符。

也可以通過查詢 information_schema.character_set 表中的記錄，來查看 MySQL 支持的字符集。SQL 語句和執行過程如下：

mysql> SELECT * FROM information_schema.character_sets; +--------------------+----------------------+---------------------------------+--------+ | CHARACTER_SET_NAME | DEFAULT_COLLATE_NAME | DESCRIPTION | MAXLEN | +--------------------+----------------------+---------------------------------+--------+ | big5 | big5_chinese_ci | Big5 Traditional Chinese | 2 | | dec8 | dec8_swedish_ci | DEC West European | 1 | | cp850 | cp850_general_ci | DOS West European | 1 | | hp8 | hp8_english_ci | HP West European | 1 | ......

可以使用 SHOW COLLATION LIKE '***'; 命令來查看相關字符集的校對規則。

mysql> SHOW COLLATION LIKE 'gbk%'; +----------------+---------+----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +----------------+---------+----+---------+----------+---------+ | gbk_chinese_ci | gbk | 28 | Yes | Yes | 1 | | gbk_bin | gbk | 87 | | Yes | 1 | +----------------+---------+----+---------+----------+---------+ 2 rows in set (0.00 sec)

上面運行結果為 GBK 字符集所對應的校對規則，其中 gbk_chinese_ci 是默認的校對規則，對大小寫不敏感。而 gbk_bin 按照二進制編碼的值進行比較，對大小寫敏感。

也可以通過查詢 information_schema.COLLATIONS 表中的記錄，來查看 MySQL 中可用的校對規則。SQL 語句和執行過程如下：

mysql> SELECT * FROM information_schema.COLLATIONS; +--------------------------+--------------------+-----+------------+-------------+---------+ | COLLATION_NAME | CHARACTER_SET_NAME | ID | IS_DEFAULT | IS_COMPILED | SORTLEN | +--------------------------+--------------------+-----+------------+-------------+---------+ | big5_chinese_ci | big5 | 1 | Yes | Yes | 1 | | big5_bin | big5 | 84 | | Yes | 1 | | dec8_swedish_ci | dec8 | 3 | Yes | Yes | 1 | | dec8_bin | dec8 | 69 | | Yes | 1 | | cp850_general_ci | cp850 | 4 | Yes | Yes | 1 | | cp850_bin | cp850 | 80 | | Yes | 1 | ......

例 1
分別指定“A”和“a”按照 gbk_chinese_ci 和 gbk_bin 校對規則進行比較。SQL 語句和運行結果如下：

mysql> SELECT CASE WHEN 'A' COLLATE gbk_chinese_ci = 'a' COLLATE gbk_chinese_ci then 1-> else 0 end; +-------------------------------------------------------------------------------------+ | CASE WHEN 'A' COLLATE gbk_chinese_ci = 'a' COLLATE gbk_chinese_ci then 1 else 0 end | +-------------------------------------------------------------------------------------+ | 1 | +-------------------------------------------------------------------------------------+ 1 row in set (0.02 sec) mysql> SELECT CASE WHEN 'A' COLLATE gbk_bin = 'a' COLLATE gbk_bin then 1-> else 0 end; +-----------------------------------------------------------------------+ | CASE WHEN 'A' COLLATE gbk_bin = 'a' COLLATE gbk_bin then 1 else 0 end | +-----------------------------------------------------------------------+ | 0 | +-----------------------------------------------------------------------+ 1 row in set (0.00 sec)

由于 gbk_chinese_ci 校對規則忽略大小寫，所以認為兩個“A“和“a”是相同的。 gbk_bin 校對規則不忽略大小寫，則認為兩個字符是不同的。

在實際應用中，我們應事先確認應用需要按照什么樣方式排序，是否區分大小寫，然后選擇相應的校對規則。

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