字符型數(shù)據(jù)
字符型數(shù)據(jù)可以使用定長(zhǎng)或變長(zhǎng)的字符串來(lái)實(shí)現(xiàn)，其不同點(diǎn)在于固定長(zhǎng)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(zhǎng)字符串不需要向右填充，并且所有字節(jié)數(shù)可變。
char 定長(zhǎng)型，字節(jié)長(zhǎng)度固定，最大長(zhǎng)度為255字節(jié)，可以使用char（20）這種方式限定長(zhǎng)度，查詢(xún)速度快，但不靈活
varchar 變長(zhǎng)型，字節(jié)長(zhǎng)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(zhǎng)度，查詢(xún)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(lèi)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(yǔ)系，比如英語(yǔ)，其中每個(gè)字母只需要1個(gè)字節(jié)來(lái)存儲(chǔ);而其他一些語(yǔ)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(lèi)字符集被稱(chēng)為多字符集
在mysql中，可以使用SHOW CAHRACTER SET語(yǔ)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)
