#!/usr/local/bin/perl -l
#
use strict;
use warnings;

my $sql = q{f1,f2, SUM(f3),CONCAT(f4,f5, f6), f7};

my @fields = split m{\s*,\s*}, $sql, 4;

splice @fields, 3, 1,
   reverse
   map { $_ = reverse }
   split m{\s*,\s*}, reverse($fields[3]), 2;

print for @fields;