David T. Ashley wrote:
> I have a table with two integer fields (call them p and q).
>
> When I insert a record with a known p, I want to choose q to be one larger
> than the largest q with that p.
>
> What is the best and most efficient way to do this?
>
> For example, let's say the table contains (p,q):
>
> 1,1
> 1,2
> 1,3
> 2,1
> 2,2
> 2,3
> 2.4
> 2,5
> 3,1
> 3,2
>
> If I insert a new record with p=2, I would want to choose q to be 6. But if
> I insert a record with p=3, I would want to choose q to be 3.
>
> Is there any alternative to locking the table, querying for max q with the
> desired p, then inserting?
>
Yes
CREATE TABLE `t` (
`p` int(10) unsigned NOT NULL default '0',
`q` int(10) unsigned NOT NULL auto_increment,
PRIMARY KEY (`p`,`q`)
) ;
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Chris W
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