MySQL - Joining multiple select statements

I initially tried fetching data using individual queries which took too much of resources, so I am trying to combine the queries in order to reduce the time taken. The first select works fine in itself but I want to combine with the second select in order to reduce the time taken.

Current error: #1241 - Operand should contain 1 column(s)

SELECT (SELECT sc.description AS description, 
           sc.maincode, 
           sc.controlcode, 
           sc.subcode, 
           ( ob.debitbalance - ob.creditbalance ) AS mainbalance 
    FROM   subcode AS sc 
           LEFT JOIN openingbalance AS ob 
                  ON ( sc.maincode = ob.maincode 
                       AND sc.controlcode = ob.controlcode 
                       AND sc.subcode = ob.subcode ) 
    GROUP  BY sc.maincode, 
              sc.controlcode, 
              sc.subcode 
    ORDER  BY sc.maincode, 
              sc.controlcode, 
              sc.subcode ASC) AS test, 
   (SELECT Sum(v.debit)                               AS totaldebit, 
           Sum(v.credit)                              AS totalcredit, 
           ( mainbalance + totaldebit - totalcredit ) AS openingbalance 
    FROM   subcode AS sc 
           LEFT JOIN voucher AS v 
                  ON ( sc.maincode = v.maincode 
                       AND sc.controlcode = v.controlcode 
                       AND sc.subcode = v.subcode ) 
    WHERE  Substring(v.voucherdate, 1, 7) < '07-2019' 
    GROUP  BY sc.maincode, 
              sc.controlcode, 
              sc.subcode 
    ORDER  BY sc.maincode, 
              sc.controlcode, 
              sc.subcode ASC) AS test2 

Table structure is as follows:

 Subcode Table
    +----------+-------------+---------+--------------+
    | Maincode | Controlcode | Subcode | Description  |
    +----------+-------------+---------+--------------+
    |       01 |          01 |     123 | Test Account |
    |       01 |          02 |     124 | Test Account |
    +----------+-------------+---------+--------------+

    Voucher Table
    +-------------+--------------+---------------+----------+-------------+---------+----------------+-------+--------+
    | Voucherdate | Vouchertype  | Vouchernumber | Maincode | Controlcode | Subcode |  Description   | Debit | Credit |
    +-------------+--------------+---------------+----------+-------------+---------+----------------+-------+--------+
    | 2019-07-13  | BV           |            01 |       01 |          01 |     123 | Entering Test  |   100 |      0 |
    | 2019-07-13  | BV           |            01 |       01 |          02 |     124 | Enterting Test |     0 |    100 |
    +-------------+--------------+---------------+----------+-------------+---------+----------------+-------+--------+

    OpeningBalance Table
    +----------+-------------+---------+--------------+---------------+
    | Maincode | Controlcode | Subcode | Debitbalance | Creditbalance |
    +----------+-------------+---------+--------------+---------------+
    |       01 |          01 |     123 |          100 |             0 |
    |       01 |          02 |     124 |          100 |             0 |
    +----------+-------------+---------+--------------+---------------+

Hoping for following outcome

+--------------+----------+-------------+---------+-------------+------------+-------------+----------------+
| Description  | Maincode | Controlcode | Subcode | Mainbalance | Totaldebit | Totalcredit | Openingbalance |
+--------------+----------+-------------+---------+-------------+------------+-------------+----------------+
| Test Account |       01 |          01 |     123 |         100 |        100 |           0 |            200 |
| Test Account |       01 |          02 |     124 |         100 |          0 |         100 |              0 |
+--------------+----------+-------------+---------+-------------+------------+-------------+----------------+

Simple inner join and a litle math should do the trick

CREATE TABLE Subcode
    (`Maincode` int, `Controlcode` int, `Subcode` int, `Description` varchar(12))
;
    
INSERT INTO Subcode
    (`Maincode`, `Controlcode`, `Subcode`, `Description`)
VALUES
    (01, 01, 123, 'Test Account'),
    (01, 02, 124, 'Test Account')
;

✓

✓

CREATE TABLE Voucher
    (`Voucherdate` Date, `Vouchertype` varchar(2), `Vouchernumber` int, `Maincode` int, `Controlcode` int, `Subcode` int, `Description` varchar(14), `Debit` int, `Credit` int)
;
    
INSERT INTO Voucher
    (`Voucherdate`, `Vouchertype`, `Vouchernumber`, `Maincode`, `Controlcode`, `Subcode`, `Description`, `Debit`, `Credit`)
VALUES
    ('2019-07-13', 'BV', 01, 01, 01, 123, 'Entering Test', 100, 0),
    ('2019-07-13', 'BV', 01, 01, 02, 124, 'Enterting Test', 0, 100)
;

✓

✓

SELECT * FROM Voucher;

Voucherdate | Vouchertype | Vouchernumber | Maincode | Controlcode | Subcode | Description    | Debit | Credit
:---------- | :---------- | ------------: | -------: | ----------: | ------: | :------------- | ----: | -----:
2019-07-13  | BV          |             1 |        1 |           1 |     123 | Entering Test  |   100 |      0
2019-07-13  | BV          |             1 |        1 |           2 |     124 | Enterting Test |     0 |    100

CREATE TABLE OpeningBalance
    (`Maincode` int, `Controlcode` int, `Subcode` int, `Debitbalance` int, `Creditbalance` int)
;
    
INSERT INTO OpeningBalance
    (`Maincode`, `Controlcode`, `Subcode`, `Debitbalance`, `Creditbalance`)
VALUES
    (01, 01, 123, 100, 0),
    (01, 02, 124, 100, 0)
;

✓

✓

SELECT 
s.Description
  ,o.Maincode
  ,o.Controlcode
  ,o.Subcode
  , o.`Debitbalance` Mainbalance
 , v.`Debit` + o.`Debitbalance` Totaldebit 
 , v.`Credit` + o.`Creditbalance` Totalcredit 
 , v.`Debit` + o.`Debitbalance` -( v.`Credit` + o.`Creditbalance`)  Openingbalance 
FROM OpeningBalance o inner Join Voucher v 
ON o.Maincode = v.Maincode AND o.Controlcode = v.Controlcode AND o.Subcode = v.Subcode
INNER JOIN Subcode s ON o.Maincode = s.Maincode AND o.Controlcode = s.Controlcode AND o.Subcode = s.Subcode
WHERE  MONTH(v.voucherdate) <= 7 AND YEAR(v.voucherdate) <= 2019

Description  | Maincode | Controlcode | Subcode | Mainbalance | Totaldebit | Totalcredit | Openingbalance
:----------- | -------: | ----------: | ------: | ----------: | ---------: | ----------: | -------------:
Test Account |        1 |           1 |     123 |         100 |        200 |           0 |            200
Test Account |        1 |           2 |     124 |         100 |        100 |         100 |              0

SELECT (SELECT sc.description AS description, 
           sc.maincode, 
           sc.controlcode, 
           sc.subcode, 
           ( ob.debitbalance - ob.creditbalance ) AS mainbalance 
    FROM   Subcode AS sc 
           LEFT JOIN OpeningBalance AS ob 
                  ON ( sc.maincode = ob.maincode 
                       AND sc.controlcode = ob.controlcode 
                       AND sc.subcode = ob.subcode ) 
    GROUP  BY sc.maincode, 
              sc.controlcode, 
              sc.subcode 
    ORDER  BY sc.maincode, 
              sc.controlcode, 
              sc.subcode ASC) AS test, 
   (SELECT Sum(v.debit)                               AS totaldebit, 
           Sum(v.credit)                              AS totalcredit, 
           ( mainbalance + totaldebit - totalcredit ) AS openingbalance 
    FROM   Subcode AS sc 
           LEFT JOIN Voucher AS v 
                  ON ( sc.maincode = v.maincode 
                       AND sc.controlcode = v.controlcode 
                       AND sc.subcode = v.subcode ) 
    WHERE  Substring(v.voucherdate, 1, 7) < '07-2019' 
    GROUP  BY sc.maincode, 
              sc.controlcode, 
              sc.subcode 
    ORDER  BY sc.maincode, 
              sc.controlcode, 
              sc.subcode ASC) AS test2 

Operand should contain 1 column(s)

SELECT Substring(voucherdate, 1, 7) FROM Voucher

| Substring(voucherdate, 1, 7) |
| :--------------------------- |
| 2019-07                      |
| 2019-07                      |

db<>fiddle here