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 result
+s)
use Data::Dumper;
$Data::Dumper::Indent = 0;
$Data::Dumper::Terse = 1;
($\, $,) = ("\n", ",\n");
print map { Dumper $_ } @out;
[download]

['KEYWORD','select'],
['KEYWORD','case'],
['KEYWORD','when'],
['WORD','a'],
'=',
['WORD','b'],
['WORD','then'],
['QUOTED','\'c\''],
['WORD','else'],
['QUOTED','\'d\''],
['KEYWORD','end'],
['DQWORD','"tough_one"'],
['COMMA',','],
['WORD','e'],
['KEYWORD','as'],
['DQUOTED','"even tougher"'],
['KEYWORD','from'],
['WORD','mytable']
[download]