how to join two query result and grouped it by a column - php

Question

i have query joined by union and it give me desirable result separately in rows i want to join those two rows and add its values but i don't know how to do it the query is
SELECT
`b`.`main_code`,
`b`.`account_title`,
SUM(CASE
WHEN
`a`.`type` = 'CP'
AND `a`.`interactive_person` = '6'
AND `a`.`date` BETWEEN '2018-02-12' AND '2018-07-31'
THEN
`a`.`balance`
ELSE 0
END) AS `credit`,
SUM(CASE
WHEN
`a`.`type` = 'CR'
AND `a`.`interactive_person` = '6'
AND `a`.`date` BETWEEN '2018-02-12' AND '2018-07-31'
THEN
`a`.`balance`
ELSE 0
END) AS `debit`,
SUM(CASE
WHEN
`a`.`type` = 'CR'
AND `a`.`interactive_person` = '6'
AND `a`.`date` BETWEEN '2018-02-12' AND '2018-07-31'
THEN
`a`.`balance`
WHEN `a`.`type` = 'CP' THEN - 1 * `a`.`balance`
ELSE 0
END) AS `balance`
FROM
`vouchers` AS `a`,
`data` AS `b`
WHERE
`a`.`interactive_person` = '6'
AND `a`.`post_status` = 'yes'
AND `a`.`interactive_person` = `b`.`main_code`
AND `a`.`date` BETWEEN '2018-02-12' AND '2018-07-31'
UNION SELECT
`b`.`main_code`,
`b`.`account_title`,
IFNULL(SUM(`a`.`debit`), 0) AS `debit`,
IFNULL(SUM(`a`.`credit`), 0) AS `credit`,
(`debit` - `credit`) AS `balance`
FROM
`journal_vouchers` AS `a`,
`data` AS `b`
WHERE
`a`.`account_id` = '44'
AND `a`.`date` BETWEEN '2018-02-12' AND '2018-07-31'
AND `post_status` = 'yes'
AND `cancel_status` = 'off'
AND `a`.`account_id` = `b`.`account_code`
GROUP BY `b`.`main_code`;
the query is a bit complex let me explain it little:
this query takes the result from 3 tables but main thing is that before union its take result from two table and after union two tables in which one table data interact with both. in short the result i get is
+-----------+---------------+--------+-------+---------+
| main_code | account_title | credit | debit | balance |
+-----------+---------------+--------+-------+---------+
| 6 | cash account | 5200 | 520 | -4680 |
+-----------+---------------+--------+-------+---------+
| 6 | cash account | 0 | 200 | -200 |
+-----------+---------------+--------+-------+---------+
i want the full query grouped by maincode but i dont know how do it
i want result to be
6 | cash account | 5200 | 320 | -4880