------------- 8< ---------
my $lexer = make_lexer(
    sub { shift @sql },  # iterator
    [ DQUOTED   => qr/"[^"]+"/     ],
    [ QUOTED    => qr/'[^']*'/     ],
    [ DQWORD    => qr/"\w+"/       ],
    [ WORD      => qr/\w+/i        ],
    [ COMMA     => qr/,/           ],
    [ SPACE     => qr/\s+/, sub {} ],
);
------------- 8< ---------

##</code><code>##

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