$dbh->connect(...);

# prepare statements
$sth->prepare("SELECT ...");
$sth2->prepare("SELECT COUNT(*) FROM table WHERE col=?");

# loop through sth results
$sth->execute;
while(($var)=$sth->fetchrow_array) {

    # select the count -- only 1 result row
    $sth2->execute($var);
    ($count)=$sth2->fetchrow_array;
    # finish() here after each fetch?
    $sth2->finish;

}
# or should finish() for sth2 be called here 
# when sth2 won't be used again?
#$sth2->finish;

$dbh->disconnect;
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finish() should be implicitly called whenever you re-execute a statement (so you could wait to call it), but I think it's better practice to just put it right after the fetch. And what you may want to do instead of the separate execute/fetch/finish statements is a single selectrow statement:

($count) = $dbh->selectrow_array( $sth2, undef, $var );
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