MySQL的字符类型

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MySQL的字符类型

字符类型

mysql> SHOW CHARACTER SET; -- 查看服务器支持的字符集
+----------+---------------------------------+---------------------+--------+
| 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 |
| utf8     | UTF-8 Unicode                   | utf8_general_ci     |      3 |
| utf8mb4  | UTF-8 Unicode                   | utf8mb4_0900_ai_ci  |      4 |
+----------+---------------------------------+---------------------+--------+
41 rows in set (0.04 sec)

校对规则

字符集内用于字符比较和排序的一套规则，以

SHOW COLLATION; -- 查看服务器支持的校对规则

基本定义

对于字符类型而言，其指定宽度均为存入宽度，以字符为单位。

mysql> create table `test` (
    -> ch char(5) not null,
    -> vc varchar(5) not null
    -> ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin；

定长变长

区别差异

mysql> select upper("justthesame"),lower("JUSTTHESAME");
+----------------------+----------------------+
| upper("justthesame") | lower("JUSTTHESAME") |
+----------------------+----------------------+
| JUSTTHESAME          | justthesame          |
+----------------------+----------------------+
1 row in set (0.00 sec)

指定量取

mysql> select left("qwert",3);
+-----------------+
| left("qwert",3) |
+-----------------+
| qwe             |
+-----------------+
1 row in set (0.00 sec)

中间字符

mysql> select mid("qwert",2,2);
+------------------+
| mid("qwert",2,2) |
+------------------+
| we               |
+------------------+
1 row in set (0.00 sec)

截取字符

mysql> select substring("qwertyui",1,4);
+---------------------------+
| substring("qwertyui",1,4) |
+---------------------------+
| qwer                      |
+---------------------------+
1 row in set (0.00 sec)

字符长度

mysql> select char_length("qwertyu");
+------------------------+
| char_length("qwertyu") |
+------------------------+
|                      7 |
+------------------------+
1 row in set (0.00 sec)

字节长度

mysql> select length("qwertyu");
+-------------------+
| length("qwertyu") |
+-------------------+
|                 7 |
+-------------------+
1 row in set (0.00 sec)

字符连接

mysql> select concat("123","abc","456","def");
+---------------------------------+
| concat("123","abc","456","def") |
+---------------------------------+
| 123abc456def                    |
+---------------------------------+
1 row in set (0.00 sec)

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