I need to know the total number of threadIDs

It's a little unclear to me from your description whether you just need to know this information, in which case you can ask the database to provide it with a GROUP BY clause, or whether you're looping through all messages anyway, and you just want to count thread IDs*. In the latter case, since I assume the thread IDs are a unique identifier per thread, you can do this with a hash. Here are examples of both:

use warnings;
use strict;
use Data::Dump;
use DBI;

# set up a dummy database
my $dbh = DBI->connect("dbi:SQLite::memory:", undef, undef,
    { RaiseError=>1 });
$dbh->do(<<'END');
CREATE TABLE messages (
    msgID INTEGER,
    threadID INTEGER
)
END
my $sth_i = $dbh->prepare(
    'INSERT INTO messages (msgID, threadID) VALUES (?,?)');
$sth_i->execute($_,$_>>4) for 0..127;

# ask the DB to give us per-thread information
dd $dbh->selectall_arrayref(
    'SELECT threadID, COUNT(*) FROM messages GROUP BY threadID');
# => [ [0, 16], [1, 16], [2, 16], [3, 16],
#      [4, 16], [5, 16], [6, 16], [7, 16], ]

# loop through rows and count threads ourselves
my $sth_s = $dbh->prepare(
    'SELECT msgID, threadID from messages');
$sth_s->execute;
my %threadIDs;
while ( my $row = $sth_s->fetchrow_hashref ) {
    $threadIDs{ $row->{threadID} }++;
}
dd \%threadIDs;
# => { "0" => 16, "1" => 16, "2" => 16, "3" => 16,
#      "4" => 16, "5" => 16, "6" => 16, "7" => 16 }

[download]

* Update: Upon rereading, it's probably the latter. By the way, $current_count_all <= $stopcount_all sounds like you want to limit the number of records returned, which you can also do in the database, e.g. in MySQL with a LIMIT clause.

Update 2: For completeness, there are two issues with the approach you showed in the OP. First, you need to be certain that $threadID doesn't ever contain the separator character ("," in this case), and your regex is too simple in that it will also match partial IDs (e.g. /234/ will match in "1234,5678"), which you'd need to prevent by anchoring the regex appropriately - for example, if the IDs are integers, you could say /\b\Q$threadID\E\b/) (note I've used \Q...\E to escape any special characters in $threadID even though I just said they're integers; it's just to play it extra safe). But the method of searching the string for the $threadID will be way less efficient than a hash, so I would always recommend that instead. Also modified the first example to supply the threadID in addition to the count.

In reply to Re: Counting fields from database (updated) by haukex
in thread Counting fields from database by htmanning

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