Rails - Feb 2006 - Migrations - How to set auto increment?

Hi all,

I''d like to know how can I set a field to auto increment in migrate 
scripts. In mysql, it''s auto_increment, and in postgresql,
it''s serial.
How can I make a migrate script which works in both places?

TIA,
Vamsee.

-- 
Posted via http://www.ruby-forum.com/.

Sorry, I forgot to tell you that I want auto increment for a field other 
than the primary key (id).

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Posted via http://www.ruby-forum.com/.

Vamsee wrote:
> Sorry, I forgot to tell you that I want auto increment for a field
> other than the primary key (id).
> 
mysql> create table test (
a int auto_increment primary key,
b int unique auto_increment
);
ERROR 1075: Incorrect table definition; There can only be one auto
column and it must be defined as a key

MySQL doesn''t seem able.