use strict;
use warnings;
use Text::Balanced qw(extract_bracketed);

sub mysplit {
    my $text = shift;
    my @fields;
    do {
        my ($paren, $post, $pre) = extract_bracketed($text, '()', '[^(]*');
        
        my $s = '';
        if ($pre) {
            $s = $pre;
        } elsif (!$paren) {
            $s = $post;
            $post = '';
        }
        $s =~ s/^,//;            # get rid of superfluous leading comma
        my @f = split /,/, $s;
        $f[-1] .= $paren if @f;  # append balanced parens part to last elem
        
        push @fields, @f;
    
        $text = $post;
    } while ($text);
    return @fields;
}

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

print "$_\n" for mysplit($sql);

##</code><code>##

f1
f2
 SUM(f3)
CONCAT(f4,f5, f6)
 f7