Thank you for the tutorial. I'm new to PERL, more used to PHP, and I'm tailoring your code and making a Postgres database of songs that I perform and write to help organise my practice. But for the life of me I can't get the prepared statement to work with my Postgres query. The "ORDER BY" clause silently fails:

my $data = $DBH->selectall_arrayref("
   select @{[join(',', @COLS)]}
   from songs
   order by ?
", undef, ($sort));
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I've tried all sorts of things, but I can't get the sort order to work, so I resorted to the following which would be open to SQL injection:

my $data = $DBH->selectall_arrayref("
   select @{[join(',', @COLS)]}
   from song
   order by $sort") or die "DBI::errstr";
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Here is some DBI->Trace output, but I can't debug the problem...

...
    STORE DBI::db=HASH(0x11c9078) 'dbi_connect_closure' => CODE(0x11c9
+7f8)
    <- STORE= ( 1 ) [1 items] at /usr/local/lib/perl/5.18.2/DBI.pm lin
+e 754 via  at /home/XXXX/.../songs_perlmonks_org/songs.cgi line 11
    -> selectall_arrayref for DBD::Pg::db (DBI::db=HASH(0x11c8f10)~0x1
+1c9078 '
   select id,title,key,recorded,songwriter,vocals_needed,length
   from song
   order by ?
' HASH(0x110dd70) 'songwriter') thr#bac010
1   -> prepare for DBD::Pg::db (DBI::db=HASH(0x11c9078)~INNER '
   select id,title,key,recorded,songwriter,vocals_needed,length
   from song
   order by ?
' HASH(0x110dd70)) thr#bac010
Begin dbd_st_prepare (statement: 
   select id,title,key,recorded,songwriter,vocals_needed,length
   from song
   order by ?
)
Begin pg_st_split_statement
End pg_st_split_statement
Immediate prepare decision: dml=1 direct=0 server_prepare=1 prepare_no
+w=0 PGLIBVERSION=90309
End dbd_st_prepare
1   <- prepare= ( DBI::st=HASH(0x110df38) ) [1 items] at /home/XXXX/..
+./songs_perlmonks_org/songs.cgi line 23
Begin dbd_bind_ph (ph_name: 1)
End dbd_bind_ph
Begin dbd_st_execute
PQexec* decision: dml=1 direct=0 server_prepare=1 numbound=0 numphs=1 
+default=0 current=0
Begin _sqlstate
End _sqlstate (imp_dbh->sqlstate: 00000)
End _sqlstate (status: 2)
End dbd_st_execute (rows: 32)
Begin dbd_st_fetch
End dbd_st_fetch
...
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