use Data::Dumper;
print GetNodes({name => "hello",type => "god", color => "greeen"});

sub GetNodes
{
    my $meta = shift;   #expects a hash of {name => value}
    print Dumper($meta);
    my $sql = "SELECT md1.node_id FROM ";
    my @From;           # list of tables
    my @Where;          # list of conditions
    my @LastWhere;
    my $i = 0;
    foreach my $name (keys %$meta)
    {
        $i ++;
        push @From, "`meta_data` as md$i";
        push @Where,"md$i.name = \"" . $name . "\"";
        push @Where,"md$i.value = \"" . $meta->{$name} . "\"";
        push @LastWhere,"md$i.node_id";
    }
    $sql .= join(",",@From) . " WHERE ";
    $sql .= join(" AND ", @Where);
    $sql .= " AND " .join(" = ",@LastWhere) . ";";
    return $sql;
}

##</code><code>##

SELECT md1.node_id
 FROM `meta_data` as md1,`meta_data` as md2,`meta_data` as md3
 WHERE md1.name = "type"
 AND md1.value = "god"
 AND md2.name = "color"
 AND md2.value = "greeen"
 AND md3.name = "name"
 AND md3.value = "hello"
 AND md1.node_id = md2.node_id = md3.node_id;