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use Data::Dumper;
print(Dumper(\%db));

foreach $key (keys(%db)) {
   for ($record_num=0; $record_num<@{$db{$key}}; $record_num++) {
...
      }
   }
}

foreach $key (keys(%db)) {
   foreach $record (@{$db{$key}}) {
...
      }
   }
}

# From ref to array of fields:
push(@{$db{$key}}, $record);
...
-or-
# From a array of fields that will change:
push(@{$db{$key}}, [ @fields ]);

# Gives:
#    key1,field1,field2,field3,field4
...
      print $key, $record_num, @{$db{$key}[$record_num]};
   }
}