mysql 数据类型详解_MySQL笔记之数据类型详解
字符型數據
字符型數據可以使用定長或變長的字符串來實現，其不同點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數;變長字符串不需要向右填充，并且所有字節數可變。
char???????????????????????? 定長型，字節長度固定，最大長度為255字節，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，字節長度隨數據量變化，最多可存儲65535字節，varchar(20)可以限定長度，查詢速度不及char，但使用靈活
如果需要存儲文本或者文檔，需要使用text類型數據，包括四種
tinytext???????????????????? 255字節
text????????????????????????? 65535字節
mediumtext???????????? 16777215字節
longtext?????????????????? 4294967295字節
以上三種在進行分組排序或者比較的時候只采用前1024字節進行比較
字符集
對于拉丁語系，比如英語，其中每個字母只需要1個字節來存儲;而其他一些語言，比如中文，包含了大量字符，每個字符的存儲需要多個字節，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,存儲一個漢字最多需要2個字節，utf8最多則需要3個
數值型數據
整數型數據
浮點型數據
數值型數據可以定義為unsigned，對整數而已可以改變其范圍，對浮點數而言可以限定其不能為負數
時間數據
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