This sequence of statements can be easier: 
$query = "select * from finalLevel3 where id=\"$ID\";";
$sth = $dbh -> prepare($query);

# I would suggest this:
my $query = $dbh->prepare("SELECT * FROM finalLevel3 WHERE id='$ID'");

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I personally like to captialize the SQL key words, but preferences vary. Also the single quote within the double quote will expand $ID just fine. There is no need for \" in this situation. I was amazed when I learned this.

I am also a bit confused about this: 

 foreach $item (@{$clusters}) {
 #.....
 }

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I would think that since you are iterating over clusters, that something like this would be more clear: 

 
foreach my $cluster (@$clusters) {                                 
#.....
}

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So when do you need the extra {}? You need this when dereferencing an indexed expression, but not a non-indexed one. You also need the extra {} to make a list from a list ref returning function. 
 
my @list = @{listRefReturningFunction()};
#also consider:
my $r = {"a" => [1,2,3,4],
         "b" => [5,6,7,8],
        };
print @{$r->{"a"}}; #prints 1234
                    #here print @$r->{"a"} won't work
                    #because this is a subscripted expression
# now with list...
my @x =(1,2,3,4);
my $xref=\@x;
print @$xref;       #prints 1234 also
                    #this works because there is no subscript

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In reply to Re^2: perl, mysql: "fetchrow_array failed: fetch() without execute()" by Marshall
in thread perl, mysql: "fetchrow_array failed: fetch() without execute()" by gojira

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