RE: Tricks with DBI

[Michalis]

in reply to Tricks with DBI

Well done. Some corrections if I may.
(a) bind_columns SHOULD be after execute has been called. As DBI's manual says, that's for maximum compatibility.
(b) You call bind_columns with four parameters (the first one been undef) while your execute only returns three (id, name and phone). While I have never used bind_columns before execute, I beleive that should fail.

My way is similar but not the same (I include just the different part):

my $sth = $dbh->prepare_cached(<<SQL);
select id, name, phone from people
where birth_month = ?
SQL

for my $month (@months) {
  print "People born in $month:\n";

  my($id, $name, $phone);
 
  # Execute the statement for this $month
  $sth->execute($month);
  $sth->bind_columns(\$id, \$name, \$phone);
  # Also valid:  $sth->bind_columns(\($id, $name, $phone));
  # Fetch each row and print out the values
  while ($sth->fetch) {
     print "\t", join("\t", $id, $name, $phone), "\n";
  }
}

[btrott]

Thanks for the suggestions. You're quite right about bind_columns being called after execute; I've been bitten by that in the past.

As for the 4 arguments to bind_columns, and the first argument being undef... I believe this is an anachronism of DBI. I just looked at the manpage, and you're right that it seems to only expect 3 arguments, now.

In the past, though, I *think* the first argument to bind_columns was supposed to be a hash ref. So I got into the habit of using undef as the first arg, because I never cared about passing anything in the hash ref. I can't find that in the DBI manpage anymore, but I did find this:

    bind_columns
        ....
        For compatibility with old scripts, if the first
        parameter is undef or a hash reference it will be
        ignored.

I don't remember what the hash ref was supposed to hold--nor would I, really, since I never actually used it. :) I always just used undef. Thanks for pointing this out.