Re: What are placeholders in DBI, and why would I want to use them?

[schweini]

I'd just like to add that extensive use of DBI-placeholders renders a CGI-app basically IMMUNE to the so-called "SQL-injection" family of attacks, which consist of shoving a bit of nasty SQL instrucions down your CGI's thraot, which it would - if it doesn't use placeholders or another escaping tactic, just pass on to the DB.
This, all by itself, is a very, very nice thing to have, i think. additionally, you can never be sure that some data you could've sworn would never contain a single-quote doesn't end up containing one some day, leaving you with a sometimes quite cryptic syntax-error.

[EvdB]

You mean that DBI queries should be written:

my $query = $dbh->prepare
    ( "select id, name from user where name = ?" );
$query->execute( $name_from_params );

Instead of:

my $query = $dbh->prepare
    ( "select id, name from user " .
      "where name = '$name_from_params'" );
$query->execute();

Couldn't agree more.

[jZed]

You have mentioned two good reasons for using placeholders - security and problems with embedded quote marks. There is a third reason which applies in many situations: placeholders, when properly placed outside of a loop save time by allowing the RDBMS to parse and optimize the SQL statement once and then execute it many times without re-parsing or re-optimizing it.