fetchrow_arrayref always returns a reference to the same array as an optimisation. This is documented. If you wish to save the data, you need to copy it.

push @qrydata, [ @$row ];
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By the way,

last if $xx++ >10;
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should be

if (@qrydata > 10) {
    $sth->finish();
    last;
}
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The counter variable is useless, and calling finish avoids a warning.

Even better would be to use a LIMIT clause to not fetch the rows you don't want in the first place. Then you'd also be able to use selectall_*.