Sorry, I posted my reply too hastily. The second parameter you pass to ->selectall_arrayref must be a hash with the key Slice, not Columns:

my $data_all =  $connection->selectall_arrayref($query, { Slice => {} 
+} );
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Then, each element of $data_all will be a hashref (not a hash as you assume):

  my $currec = $row;
  foreach my $columns (keys %$currec){
    say $columns;
    say $currec{$columns};
  }
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Whenever you're in doubt about a data structure, consider using Data::Dumper to print it:

use Data::Dumper;
say Dumper $row;
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