Dynamic query generation

chanakya has asked for the wisdom of the Perl Monks concerning the following question:

Greetings!
I'm trying to build a query based on a "Action". The Action value comes from a SELECT query.

I have a hash which contains the database field names and there equivalent values (These values will be populated by a SELECT query).
I want to build a query from this hash based on the "Action" value.
For example if the "Action" is "Problem Submit", I'd like a build a query like

INSERT INTO Ticket_Data(Data_id, Prov_id, Provclientid) VALUES (Ticket
+_Data_seq.nextval, 'EECO::UTN:BPL', 'BPC::123');
[download]

All the other fields needs to be skipped if the Action is "Problem Submit"(other than Data_id, Prov_id, Provclientid)

I'm trying to achieve the same using the code below, but could not get the values while building the query.
The reason being, to skip some of the fields I need to traverse the hash using a foreach() loop, once done I've to
append the values outside the foreach() loop to the main query.

Could anyone throw some light about how to achieve the above said functionality.


$query = $dbh->prepare(qq{SELECT * from table_name});
...
my $data = $query->fetchrow_hashref;
...

%MAPPING = (
        
        'Data_id' => 'Ticket_Data_seq.nextval',
        'Action' => "Problem Submit",
        'Cust_Ticket_Number' => "",
        'Our_Ticket_Number' => "$data->{'TicketNumber'}",
        'msg_id' =>    "",
        'time_stamp'     =>    "",
        'Description' =>    "",
        'EL_Edesc' =>    "",
        'prov_id' =>    "EECO::UTN::BPL",
        'provclientid' => "BPC::123",
        'prov_client_org' =>    "",
        'prov_client_buz' =>    "",
        'prov_schema_type' =>    ""
        );
        

if ($action eq 'Problem Submit')        
  my $query = "INSERT INTO Ticket_Data (";

  for  $key ( keys %ORA_MAPPING ) {
     $value = $ORA_MAPPING{$key};
     next if $key eq "Data_id";
    $q.=" $key, ";

  }

  $query .= " ) VALUES ($ORA_MAPPING{$_} )";

} elsif ($action eq 'Update') {
...
}
[download]

!!@!!
May the force be with you!!

Comment on Dynamic query generation Select or Download Code

Replies are listed 'Best First'.
Re: Dynamic query generation by Joost (Canon) on May 05, 2005 at 10:32 UTC
You should be using strict. I think `$q.="$key, ";` should be `$query.="$key, ";` update: and you're creating a new lexical variable $query within the `if ($action eq ...`, which goes out of scope. `my $query; if ($action eq 'Problem Submit') $query = "INSERT INTO Ticket_Data ("; for $key ( keys %ORA_MAPPING ) { my $value = $ORA_MAPPING{$key}; next if $key eq "Data_id"; $query.=" $value, "; # or did you really mean $key here? }` [download] Also note that you should be careful if you build queries from external/dynamic input. Use placeholders if you can, and DBI->quote otherwise. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l] [select]
Re^2: Dynamic query generation by chanakya (Friar) on May 05, 2005 at 12:19 UTC
Joost Thanks for pointing out the error, Here's the updated code %ORA_MAPPING = ( 'Data_id' => 'Ticket_Data_seq.nextval', 'Action' => "Problem Submit", 'Cust_Ticket_Number' => "", 'Our_Ticket_Number' => "$data->{'TicketNumber'}", 'msg_id' => "", 'time_stamp' => "", 'Description' => "", 'EL_Edesc' => "", 'prov_id' => "EECO::UTN::BPL", 'provclientid' => "BPC::123", 'prov_client_org' => "", 'prov_client_buz' => "", 'prov_schema_type' => "" ); my $query = "INSERT INTO Ticket_Data ("; if ($action eq 'Problem Submit') for $key ( keys %ORA_MAPPING ) { $value = $ORA_MAPPING{$key}; next if $key eq "Data_id"; $query .=" $key, "; } $query .= " ) VALUES ($ORA_MAPPING{$_} )"; } elsif ($action eq 'Update') { ... } [download] Is it possible to build the query using the above code or is there any other better approach. I'd like to know that approach as well. Many thanks for your time	[reply] [d/l]
Re: Dynamic query generation by polettix (Vicar) on May 05, 2005 at 10:52 UTC
In addition to Joost's correct comments, also be careful to use the same identifier `$query` to represent semantically different concepts: at the very beginning it's a statement handle object, while it becomes a string containing the query to be executed later. I also don't entirely get the meaning of `MAPPING`, which automagically becomes `ORA_MAPPING` inside the cycle - this definitevely poses a requirement to you: `use strict` :) Flavio (perl -e 'print(scalar(reverse("\nti.xittelop\@oivalf")))') Don't fool yourself.	[reply] [d/l] [select]
Re: Dynamic query generation by ghenry (Vicar) on May 06, 2005 at 09:58 UTC
Have you thought about TRIGGERS? I may be missing the point slightly though. Walking the road to enlightenment... I found a penguin and a camel on the way..... Fancy a yourname@perl.me.uk? Just ask!!!	[reply]