I'm curious if you are required to use fetchall_hashref or if you can use fetchall_arrayref instead.

For example, to get an array of hashes containing the rows in the same order they are produced by your query, you could do this:

my $clients = $get->fetchall_arrayref({});
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Now $clients is a reference to an array, sorted by last name, where each element is a hash containing the row data.

If you want a list of IDs ordered by last name:

my @ids = map { $_->{id} } @$clients;
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If you want a hash that maps IDs to clients:

my %client_for = map { $_->{id} => $_ } @$clients;
# $client_for->{1}->{lastname} ...
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Let me know if this helps and if you have any more questions.