MyISAM has this really cool feature where you can specify autoincrement
on a secondary column in a multiple column index. In such a case the
generated value for the autoincrement column is calculated as
MAX(autoincrement column) + 1 WHERE prefix='given-prefix'. For more
refer to
http://dev.mysql.com/doc/refman/5.0/en/example-auto-increment.html. This
is exactly what I want, however I have an InnoDB table so this will not
work (in an InnoDB table, you cannot specify autoincrement on a
secondary column). So what I wanted to know was if there is some easy
way to mimic that behavior. In my last mail that I sent, in order to
mimic that functionality on InnoDB, I had to write several statements
that possibly need to be a part of a transaction. Of course that also
meant that I cannot specify that column as an autoincrement but instead
specify it something as INT NOT NULL.
Thanks
Aveek
Johan De Meersman wrote:
On Thu, Apr 22, 2010 at 12:09 PM, Aveek Misra <ave...@yahoo-inc.com> wrote:
I am not sure I understand. If I make the autoincrement column as part of
the primary key as (rev + cluster + file), how do I ensure that a reset of
the revision number is done as soon as (cluster + file) combination changes?
You want the autoincrement to go up every time you change the values in your
primary key ?
Aside from it not being a recommended practice, to put it mildly, that you
update primary key values (possible referential inconsistency), I'm not
aware of this behaviour in MyISAM, either.
An autoincrement is assigned if, and only if you assign NULL or (zero) to an
autoincrement column during an insert.
If your application behaves differently, it is probably already done either
in the application, or possibly through the use of triggers.
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