Some Terse Perl Code to Manipulate an Array, Explained

Perl still rocks. People still say it's hard to read (true), but it's because the language is terse.

sub getAccountIdsOfSitesToSuspend
    $sql = <<EOQ;
        SELECT account_id
        FROM account
            account.account_balance < (SELECT triggerAmount FROM fk_suspension_rules)
            AND (
                    SELECT IF(SUM(transaction_ammount), SUM(transaction_ammount), 0)
                    FROM transaction
                    WHERE transaction_date > DATE_SUB( CURDATE(),
                        INTERVAL (SELECT paymentWindow FROM fk_suspension_rules) DAY)
                    AND transaction.account_id = account.account_id
                ) &lt; FLOOR( -account.account_balance * (SELECT releaseFraction FROM fk_suspension_rules))
            AND (
                    SELECT IF(COUNT(*), TRUE, FALSE )
                    FROM fk_domains
                    WHERE account_id = account.account_id
                    AND never_suspend<>'y'
    $sth = $dbh->prepare($sql);
    my @result = ();
    map { push @result, $_->[0]; } @{ $sth->fetchall_arrayref([0]) };
    return @result;

This function runs an SQL statement, and then returns the result. It could be shorter, yes, but it has a nice way of collapsing a loop into a one-liner: map { push @result, $_->[0]; } @{ $sth->fetchall_arrayref([0]) };

map { ... } @ar -- this applies the code in the brackets to every element in array @ar.

@{ ... } -- dereferences the array reference returned in the brackets into an array.

fetchall_arrayref([0]) -- gets all the results from the query, slicing array element 0 from the results.

The syntax is ugly, but explicit (if you know perl).