Mysql必读MySQL笔记之数据类型详解
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《Mysql必读MySQL笔记之数据类型详解》要点： MYSQL学习字符型数据 MYSQL学习字符型数据可以使用定长或变长的字符串来实现,其不同点在于固定长度的字符串使用空格向右填充,以保证占用同样的字节数;变长字符串不需要向右填充,并且所有字节数可变. MYSQL学习char???????????????????????? 定长型,字节长度固定,最大长度为255字节,可以使用char(20)这种方式限定长度,查询速度快,但不灵活 MYSQL学习varchar??????????????????? 变长型,字节长度随数据量变化,最多可存储65535字节,varchar(20)可以限定长度,查询速度不及char,但使用灵活 MYSQL学习如果需要存储文本或者文档,需要使用text类型数据,包括四种 MYSQL学习tinytext???????????????????? 255字节 MYSQL学习text????????????????????????? 65535字节 MYSQL学习mediumtext???????????? 16777215字节 MYSQL学习longtext?????????????????? 4294967295字节 MYSQL学习以上三种在进行分组排序或者比较的时候只采用前1024字节进行比较 MYSQL学习字符集 MYSQL学习对于拉丁语系,比如英语,其中每个字母只需要1个字节来存储;而其他一些语言,比如中文,包含了大量字符,每个字符的存储需要多个字节,因此这类字符集被称为多字符集 MYSQL学习在mysql中,可以使用SHOW CAHRACTER SET语句查看字符集 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则代表此行为多字符集,比如gb2312,存储一个汉字最多需要2个字节,utf8最多则需要3个 MYSQL学习数值型数据 MYSQL学习整数型数据 MYSQL学习
MYSQL学习浮点型数据 MYSQL学习
MYSQL学习数值型数据可以定义为unsigned,对整数而已可以改变其范围,对浮点数而言可以限定其不能为负数 MYSQL学习? MYSQL学习时间数据 MYSQL学习
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