use strict;
my $sql = <<'--SQL--';
select case
  when a=b then 'c'
  else 'd'
  end "tough_one",
  e as "even tougher"
from mytable
--SQL--

use HOP::Lexer 'make_lexer';
my @sql   = $sql;
my $lexer = make_lexer(
    sub { shift @sql },  # iterator
    [ DQWORD    => qr/"\w+"/                     ],
    [ DQUOTED   => qr/"[^"]+"/                   ],
    [ QUOTED    => qr/'[^']*'/                   ],
    [ KEYWORD    => qr/\b(?:SELECT|FROM|AS|CASE|WHEN|END)\b/i  ],
    [ WORD      => qr/\w+/i                      ],
    [ COMMA     => qr/,/                         ],
    [ SPACE     => qr/\s+/, sub {}               ],
);

# parse
my @out;
push @out, $_ while $_ = $lexer->();

# Data::Dump the output (elaborated in order to produce compact results)
use Data::Dumper;
$Data::Dumper::Indent = 0;
$Data::Dumper::Terse = 1;
($\, $,) = ("\n", ",\n");
print map { Dumper $_ } @out;