字符型數(shù)據(jù)

字符型數(shù)據(jù)可以使用定長或變長的字符串來實(shí)現(xiàn)，其不同點(diǎn)在于固定長度的字符串使用空格向右填充，以保證占用同樣的字節(jié)數(shù);變長字符串不需要向右填充，并且所有字節(jié)數(shù)可變。

char???????????????????????? 定長型，字節(jié)長度固定，最大長度為255字節(jié)，可以使用char(20)這種方式限定長度，查詢速度快，但不靈活

varchar??????????????????? 變長型，字節(jié)長度隨數(shù)據(jù)量變化，最多可存儲(chǔ)65535字節(jié)，varchar(20)可以限定長度，查詢速度不及char，但使用靈活

如果需要存儲(chǔ)文本或者文檔，需要使用text類型數(shù)據(jù)，包括四種

tinytext???????????????????? 255字節(jié)

text????????????????????????? 65535字節(jié)

mediumtext???????????? 16777215字節(jié)

longtext?????????????????? 4294967295字節(jié)

以上三種在進(jìn)行分組排序或者比較的時(shí)候只采用前1024字節(jié)進(jìn)行比較

字符集

對(duì)于拉丁語系，比如英語，其中每個(gè)字母只需要1個(gè)字節(jié)來存儲(chǔ);而其他一些語言，比如中文，包含了大量字符，每個(gè)字符的存儲(chǔ)需要多個(gè)字節(jié)，因此這類字符集被稱為多字符集

在mysql中，可以使用SHOW CAHRACTER SET語句查看字符集

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 |

+----------+-----------------------------+---------------------+--------+

rows in set (0.00 sec)

其中Maxlen列大于1則代表此行為多字符集，比如gb2312,存儲(chǔ)一個(gè)漢字最多需要2個(gè)字節(jié)，utf8最多則需要3個(gè)

數(shù)值型數(shù)據(jù)

整數(shù)型數(shù)據(jù)

浮點(diǎn)型數(shù)據(jù)

數(shù)值型數(shù)據(jù)可以定義為unsigned，對(duì)整數(shù)而已可以改變其范圍，對(duì)浮點(diǎn)數(shù)而言可以限定其不能為負(fù)數(shù)

時(shí)間數(shù)據(jù)

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