mysql两列主键，具有自动增量

如果您使用的是myisam

http://dev.mysql.com/doc/refman/5.0/en/example-auto-
increment.html

对于MyISAM和BDB表，可以在多列索引的第二列上指定AUTO_INCREMENT。在这种情况下，将为AUTO_INCREMENT列生成的值计算为MAX（auto_increment_column）+
1 WHERe prefix = given-prefix。当您要将数据放入有序组中时，这很有用。

CREATE TABLE animals (    grp ENUM('fish','mammal','bird') NOT NULL,    id MEDIUMINT NOT NULL AUTO_INCREMENT,    name CHAr(30) NOT NULL,    PRIMARY KEY (grp,id)) ENGINE=MyISAM;INSERT INTO animals (grp,name) VALUES    ('mammal','dog'),('mammal','cat'),    ('bird','penguin'),('fish','lax'),('mammal','whale'),    ('bird','ostrich');SELECt * FROM animals ORDER BY grp,id;Which returns:+--------+----+---------+| grp    | id | name    |+--------+----+---------+| fish   |  1 | lax     || mammal |  1 | dog     || mammal |  2 | cat     || mammal |  3 | whale   || bird   |  1 | penguin || bird   |  2 | ostrich |+--------+----+---------+

例如：

mysql> CREATE TABLE mytable (    ->     table_id MEDIUMINT NOT NULL AUTO_INCREMENT,    ->     database_id MEDIUMINT NOT NULL,    ->     other_column CHAr(30) NOT NULL,    ->     PRIMARY KEY (database_id,table_id)    -> ) ENGINE=MyISAM;Query OK, 0 rows affected (0.03 sec)mysql> INSERT INTO mytable (database_id, other_column) VALUES    ->     (1,'Foo'),(1,'Bar'),(2,'Baz'),(1,'Bam'),(2,'Zam'),(3,'Zoo');Query OK, 6 rows affected (0.00 sec)Records: 6  Duplicates: 0  Warnings: 0mysql> SELECt * FROM mytable ORDER BY database_id,table_id;+----------+-------------+--------------+| table_id | database_id | other_column |+----------+-------------+--------------+|        1 |1 | Foo          ||        2 |1 | Bar          ||        3 |1 | Bam          ||        1 |2 | Baz          ||        2 |2 | Zam          ||        1 |3 | Zoo          |+----------+-------------+--------------+6 rows in set (0.00 sec)