...whether such a query syntax exists as either a published spec...

(I'm assuming you're after SQL syntax here, tho its not explicitly stated)

Tho not directly Perl related, there are implementations, and (conveniently) O'Reilly appears to have provided an answer as an online sample chapter for the SQL Pocket Guide.

You may also find that careful use of GROUP BY will accomplish much of what you're trying to do, albeit with some duplicate info in the rows.

A quick Google of "sql hierarchical queries" generates quite a few related hits, as does "sql tree queries", so you've got some websifting to do...

i guess, this will not exist, because it is actually a combination of querying data from a database and displaying the result.

That is one way of evaluating the problem, however it is possible to 'rethink' the situation if you strip away pre-existing paradigms, methodologies, and ask the following:

Given this:

sitcom/simpsons/homer/simpson
sitcom/simpsons/ned/flanders
sitcom/flintstones/fred/flintstone
sitcom/flintstones/wilma/flintstone
sitcom/flintstones/barney/rubble
gameshow/price is right/bob/barker
gameshow/jeopardy/alex/trebek
[download]

What can I use to transform it into this?:

$dataroot = {
  'gameshow' => {
      'price is right' => [
            {
              'lname' => 'barker',
              'fname' => 'bob'
            }
                          ],
      'jeopardy' => [
          {
            'lname' => 'trebek',
            'fname' => 'alex'
          }
                    ]
    },
  'sitcom' => {
    'simpsons' => [
        {
          'lname' => 'simpson',
          'fname' => 'homer'
        },
        {
          'lname' => 'flanders',
          'fname' => 'ned'
        }
                  ],
    'flintstones' => [
       {
         'lname' => 'flintstone',
         'fname' => 'fred'
       },
       {
         'lname' => 'flintstone',
         'fname' => 'wilma'
       },
       {
         'lname' => 'rubble',
         'fname' => 'barney'
       }
                     ]
    }
};
[download]

The key consideration here is a simple question of transforming the flat 'row-based' representation into a 'nested representation'. This does not necessarily involve a database at all. Nor does it necessarily involve 'displaying' anything (unless you count using Data::Dumper to show the output for illustrative purposes only).

=oQDlNWYsBHI5JXZ2VGIulGIlJXYgQkUPxEIlhGdgY2bgMXZ5VGIlhGV

Try this:

#! perl -slw
use strict;
use List::Util qw[ reduce ];
use Data::Dumper;

my %data;

while( <DATA> ) {
    my( $genre, $title, $fname, $lname ) = split '/';
    $data{ $genre } = {} unless exists $data{ $genre };
    $data{ $genre }{ $title } = [] unless exists $data{ $genre }{ $tit
+le };
    push @{ $data{ $genre }{ $title } }, { fname => $fname, lname => $
+lname };
};

print Dumper \%data;

__DATA__
sitcom/simpsons/homer/simpson
sitcom/simpsons/ned/flanders
sitcom/flintstones/fred/flintstone
sitcom/flintstones/wilma/flintstone
sitcom/flintstones/barney/rubble
gameshow/price is right/bob/barker
gameshow/jeopardy/alex/trebek
[download]

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

Just to refocus on the OP, the question was, (given the example 'one-off' solution that BrowserUk illustrated for this specific example, and considering the similarly-coded 'one-off' solutions by the OP in the past) where does there exist a "general purpose" mechanism to further abstract the process of doing this kind of transformation, such that there is no need to modify the 'one-off' code every time someone wants a different 'pivot' of the data structure.

The question is now mostly academic, since the humble aspirant has gone on to code a solution himself, absent a preexisting and obvious choice out there.

It is called 'vpath_pivot', named after the 'pivot table' feature found in spreadsheet software. It generates arbitrarily-nested tree structures using perl data variables, constructed from queries like:

### 1: provides same output as BrowserUk example
TREE_SELECT genre,title,fname,lname
FROM        tvshow
WITH_LEVELS ('genre','title'  )
WITH_RECORD ( 'lname','fname' )

### 2: a different 'pivot' of the same data
TREE_SELECT title,genre,fname,lname
FROM        tvshow
WITH_LEVELS ('title','genre','lname'  )
WITH_RECORD ( 'fname' )
WHERE genre != 'gameshow'

### 3: another tree 'pivot' (more compact)
TREE_SELECT title,fname,lname
FROM        tvshow
WITH_LEVELS ('title'  )
WITH_RECORD ( 'fname','lname' )
[download]

NOTE: the above is not SQL, it just looks similar for readability.

NOTE: the main approach here is to give the user the ability to 'slice and dice' the 'flat' data into different 'tree structures' all within a simple syntax (i.e., no need to re-edit the perl code).

tyvm for the replies
=oQDlNWYsBHI5JXZ2VGIulGIlJXYgQkUPxEIlhGdgY2bgMXZ5VGIlhGV