Codeigniter 4 Complex UNION queries - php

Question

I am new to Codeigniter 4 and trying to write SELECT UNION SQL Statements. According to the user guide in codeigniter 4, there is a second parameter in select() method that allows to write custom SQL Statements by setting it to false. Unfortunately it is not working. Can someone help please? Is there any alternate solution?
$query = "SELECT acnt_id, acnt_opbal as sum_amount
FROM accounts
WHERE acnt_id = '" . $acnt_id . "'
UNION
SELECT txn_acnt_id_dr as acnt_id, SUM(txn_amount_dr) as sum_amount
FROM transactions
WHERE txn_acnt_id_dr = '" . $acnt_id . "'
AND txn_date < '" . $fdate . "'
GROUP BY txn_acnt_id_dr
UNION
SELECT txn_acnt_id_cr as acnt_id, -SUM(txn_amount_cr) as sum_amount
FROM transactions
WHERE txn_acnt_id_cr = '" . $acnt_id . "'
AND txn_date < '" . $fdate . "'
GROUP BY txn_acnt_id_cr";
$result = $this->builder()->select($query, false)->get()->getResult();

Answer 1

According to CodeIgniter 4 Documentation ->getResult() should be used after building the query in order to produce your query
<?php
$builder = $db->table('mytable');
$query = $builder->get(); // Produces: SELECT * FROM mytable
foreach ($query->getResult() as $row) {
echo $row->title;
}
Addapting this to your code you'll get:
<?php
$builder = $this->builder()->select($query, false);
$query = $builder->get();
$result = $query->getResult();
Or make it all 1 line you can use Covariance and Contravariance:
$result = ($this->builder()->select($query, false)->get())->getResult();