#prepare
my $sth = $dbh->prepare('SELECT * FROM people WHERE lastname = ? AND firstname = ?');

#execute with list of bindvars
$sth->execute( $lastname, $firstname );
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But it's a bit cumbersome to adjust the bind values if the order changes.

##</code><code>##


$dbh->{pg_placeholder_dollaronly} = 1; # default is 0
my $sth = $dbh->prepare('SELECT * FROM people WHERE lastname = $1 AND firstname = $2');