Question

I’m writing a web app in Perl using Dancer framework. The database is in sqlite and I use DBI for database interaction.

I’m fine with select statements, but I wonder is there a way to count selected rows.

E.g. I have

get '/' => sub {
    my $content = database->prepare(sprintf("SELECT * FROM content LIMIT %d",
            $CONTNUM));
    $content->execute;
    print(Dumper($content->fetchall_arrayref));
};

How do I count all items in the result without issuing another query?

What I want to achieve this way is showing 30 items per page and knowing how many pages there would be. Of course I can run SELECT COUNT (*) foo bar, but it looks wrong and redundant to me. I’m looking for a more or less general, DRY and not too heavy on database way to do so.

Any SQL or Perl hack or a hint what should I read about would be appreciated.

// I know using string concatenation for querys is bad

Answer 1

You have to do it the hard way: one query to get the count and another to get your desired slice of the row set:

my $count = $database->prepare('SELECT COUNT(*) FROM content');
$count->execute();
my $n = $count->fetchall_arrayref()->[0][0];

my $content = $database->prepare('SELECT * FROM content LIMIT ?');
$content->execute($CONTNUM);
#...