MYSQL 比较集

1、什么是较对集合:字符集的字符比较规则（collation,collate），一个字符集有多个较对集合。

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mysql> create table ss (id int primary key auto_increment,

    -> cc char(10));

insert into ss values (null,"a");

insert into ss values (null,"A");

insert into ss values (null,"b");

insert into ss values (null,"B");

-------------------------------------------------------------

mysql> select * from ss order by cc asc;

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

| id | cc   |

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

|  1 | a    |

|  2 | A    |

|  3 | b    |

|  4 | B    |

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

 mysql> select * from ss order by cc desc;

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

| id | cc   |

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

|  3 | b    |

|  4 | B    |

|  1 | a    |

|  2 | A    |