Need to swap primary keys - does mysql have a way?

[matt snider]

Hey all, I couldn't find this in the cookbook.

I need to swap the primary keys of two elements. My technique is to pick an absurdly large primary key value and change elem1 to that, then change elem2 pk to the pk for elem1, then change elem1 pk to the pk of elem2.

$pk = 10;
$pk2 = 5;
$tpk = 99999999 - $pk;

$mysql->update( $table, "pk = $tpk ", "pk = ".$pk);
$mysql->update( $table, "pk = ".$pk, "pk = ".$idpk2);
$mysql->update( $table, "pk = $pk2", "pk = ".$tpk);

However, this causes the autoincrement feature to start incrementing in the absurdly high numbers, which defeats the purpose of choosing such a number.

a) is there a function that swaps the pk's of two elements in mysql?

or b) is there a way to reset the autoincrement feature back to the low numbers after the swap?

or c) is there a way to randomly get a pk from the database, that isn't already in use?