SELECT Rating, AVG(Downloads)
  FROM Test_Table
  GROUP BY Rating

#!/usr/bin/env perl
use warnings;
use strict;
use 5.10.1;
use DBI;

my $db = 'TestDatabase';
my $dbh = DBI->connect( "dbi:SQLite:dbname=$db", "", "", { RaiseError => 1, PrintError => 0 } ) or die DBI->errstr;
my $table = 'Test_Table';
$dbh->do( "DROP TABLE IF EXISTS $table" );
$dbh->do( "CREATE TABLE $table ( Id INTEGER PRIMARY KEY, Rating TEXT, Downloads INTEGER )" );
my $sth = $dbh->prepare( "INSERT INTO $table ( Id, Rating, Downloads ) VALUES ( ?, ?, ? )" );

$sth->execute( undef, "2.0", 7449 );
$sth->execute( undef, "2.7", 7048 );
$sth->execute( undef, "2.4", 4877 );
$sth->execute( undef, "3.0", 10486 );
$sth->execute( undef, "3.1", 8119 );
$sth->execute( undef, "3.0", 10706 );
$sth->execute( undef, "2.8", 4795 );
$sth->execute( undef, "3.8", 5879 );
$sth->execute( undef, "4.1", 7252 );
$sth->execute( undef, "3.6", 6259 );
$sth->execute( undef, "2.8", 6615 );
$sth->execute( undef, "4.9", 5275 );
$sth->execute( undef, undef, 3638 );
$sth->execute( undef, undef, 3690 );
$sth->execute( undef, undef, 3283 );
$sth->execute( undef, undef, 2568 );
$sth->execute( undef, "3.2", 4950 );
$sth->execute( undef, undef, 3211 );
$sth->execute( undef, undef, 3876 );
$sth->execute( undef, undef, 2308 );
$sth->execute( undef, "3.2", 3864 );
$sth->execute( undef, "4.8", 18707 );
$sth->execute( undef, undef, 3395 );
$sth->execute( undef, undef, 2927 );
$sth->execute( undef, "1.8", 2291 );
$sth->execute( undef, "4.1", 7252 );
$sth->execute( undef, "3.6", 6259 );
$sth->execute( undef, "2.8", 6615 );
$sth->execute( undef, "4.9", 5275 );
$sth->execute( undef, undef, 3638 );
$sth->execute( undef, undef, 3690 );
$sth->execute( undef, undef, 3283 );
$sth->execute( undef, undef, 2568 );
$sth->execute( undef, "3.2", 4950 );
$sth->execute( undef, undef, 3211 );
$sth->execute( undef, undef, 3876 );