There are a couple of problems here.

The basic problem is that this only tells you what the last ID in the table was (+1), not what the next ID will be. If I insert a record and then delete it, that ID will not be reused, but your solution assumes it will. The next ID will actually be the highest +2. I could do this with any number of records.

The other problem is in your second solution:

my $data = qq(SELECT id FROM table ORDER BY id DESC); # +1
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This selects every row in the table. You really want to select only one:

my $data = qq(SELECT id FROM table ORDER BY id DESC LIMIT 1); # +1
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...but this still suffers from the first problem.