mysql的collation大致的意思就是字符序。首先字符本来是不分大小的，那么对字符的>, = , < 操作就需要有个字符序的规则。collation做的就是这个事情，你可以对表进行字符序的设置，也可以单独对某个字段进行字符序的设置。一个字符类型，它的字符序有多个，比如：
下面是UTF8对应的字符序。
utf8_general_ci utf8 33 Yes Yes 1
utf8_bin utf8 83 Yes 1
utf8_unicode_ci utf8 192 Yes 8
utf8_icelandic_ci utf8 193 Yes 8
utf8_latvian_ci utf8 194 Yes 8
utf8_romanian_ci utf8 195 Yes 8
utf8_slovenian_ci utf8 196 Yes 8
utf8_polish_ci utf8 197 Yes 8
utf8_estonian_ci utf8 198 Yes 8
utf8_spanish_ci utf8 199 Yes 8
utf8_swedish_ci utf8 200 Yes 8
utf8_turkish_ci utf8 201 Yes 8
utf8_czech_ci utf8 202 Yes 8
utf8_danish_ci utf8 203 Yes 8
utf8_lithuanian_ci utf8 204 Yes 8
utf8_slovak_ci utf8 205 Yes 8
utf8_spanish2_ci utf8 206 Yes 8
utf8_roman_ci utf8 207 Yes 8
utf8_persian_ci utf8 208 Yes 8
utf8_esperanto_ci utf8 209 Yes 8
utf8_hungarian_ci utf8 210 Yes 8
utf8_sinhala_ci utf8 211 Yes 8
utf8_german2_ci utf8 212 Yes 8
utf8_croatian_ci utf8 213 Yes 8
utf8_unicode_520_ci utf8 214 Yes 8
utf8_vietnamese_ci utf8 215 Yes 8
utf8_general_mysql500_ci utf8 223 Yes 1
mysql的字符序遵从命名惯例。以_ci(表示大小写不敏感)，以_cs(表示大小写敏感)，以_bin(表示用编码值进行比较)。比如：
CREATE TABLE `issue_message` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`content` varchar(255) NOT NULL,
PRIMARY KEY (`id`),
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
这个表下面的两个sql会出现同样的结果
select * from issue_message where content = 'Yes'
select * from issue_message where content = 'yes'
如果改成下面的定义：
CREATE TABLE `issue_message` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`content` varchar(255) NOT NULL COLLATE utf8_bin,
PRIMARY KEY (`id`),
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
那么两个sql结果就会不一样了
所以，如果对字符大小敏感的话，最好将数据库中默认的utf8_general_ci设置为utf8_bin。
