mysql - MySQL - 複数の選択ステートメントを結合する

Question

最初はリソースを取りすぎた個々のクエリを使用してデータを取得しようとしたため、時間を短縮するためにクエリを組み合わせようとしています。最初の選択自体は問題なく機能しますが、時間を短縮するために 2 番目の選択と組み合わせたいと考えています。

現在のエラー: #1241 - オペランドには 1 列を含める必要があります

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 

テーブル構造は次のとおりです。

 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 |
    +----------+-------------+---------+--------------+---------------+

次の結果に期待

+--------------+----------+-------------+---------+-------------+------------+-------------+----------------+
| 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 |
+--------------+----------+-------------+---------+-------------+------------+-------------+----------------+