composit index and possible keys specific query


i have query like this

select
    date_format(referencedate, '%m/%d/%Y') as PostingDate,
    reference_code,
    "" as DocNo,
    Account_Number,
    detail_desc as Description,
    case
        when DEBT_CREDIT = "D" then sum(SF2356896(value_result, 'E77420A8EE606B00', '10011010100010011011', transact_code))
        else 0
    end as Debit,
    case
        when DEBT_CREDIT = "C" then sum(SF2356896(value_result, 'E77420A8EE606B00', '10011010100010011011', transact_code))
        else 0
    end as Credit,
    left(substring_index(COSTCENTER_CODE, "_", 1),
    9) as job,
    mid(substring_index(COSTCENTER_CODE, "_", 1), 10, length(substring_index(COSTCENTER_CODE, "_", 1))) as jobtask
from
    TPYDJOURNALTRANS_INTERCO_EMP
where
    reference_code = '202007'
    and BUSINESS_UNIT = 'XXX'
    and journal_code = 'JMTHOPERATOR'
group by
    reference_code,
    substring_index(COSTCENTER_CODE, "_", 1),
    account_number,
    detail_desc,
    DEBT_CREDIT

when i explain this query i got results like this

*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: TPYDJOURNALTRANS_INTERCO_EMP
         type: ref
possible_keys: idx_tpydjournaltrans_ie_BUSINESSUNIT2,idx_tpydjournaltrans_ie_journalcode,idx_tpydjournaltrans_ie_reference_code,idx_tpydjournaltrans_ie_BUSINESSUNIT
          key: idx_tpydjournaltrans_ie_BUSINESSUNIT
      key_len: 139
          ref: const,const,const
         rows: 1160572
        Extra: Using index condition; Using where; Using temporary; Using filesort

and this index on table TPYDJOURNALTRANS_INTERCO_EMP

---------+
| Table                        | Non_unique | Key_name                               | Seq_in_index | Column_name     | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+------------------------------+------------+----------------------------------------+--------------+-----------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| tpydjournaltrans_interco_emp |          1 | ix_tuned_transiss_tuned4               |            1 | period_code     | A         |         972 |     NULL | NULL   | YES  | BTREE      |         |               |
| tpydjournaltrans_interco_emp |          1 | ix_tuned_transiss_tuned4               |            2 | processdate     | A         |        2436 |     NULL | NULL   | YES  | BTREE      |         |               |
| tpydjournaltrans_interco_emp |          1 | ix_tuned_transiss_tuned4               |            3 | journal_code    | A         |        2436 |     NULL | NULL   | YES  | BTREE      |         |               |
| tpydjournaltrans_interco_emp |          1 | ix_tuned_transiss_tuned4               |            4 | account_number  | A         |       27269 |     NULL | NULL   | YES  | BTREE      |         |               |
| tpydjournaltrans_interco_emp |          1 | ix_tuned_transiss_tuned4               |            5 | debt_credit     | A         |       20019 |     NULL | NULL   | YES  | BTREE      |         |               |
| tpydjournaltrans_interco_emp |          1 | ix_tuned_transiss_tuned4               |            6 | costcenter_code | A         |      441773 |     NULL | NULL   | YES  | BTREE      |         |               |
| tpydjournaltrans_interco_emp |          1 | ix_tuned_transiss_tuned4               |            7 | detail_desc     | A         |     1656648 |     NULL | NULL   | YES  | BTREE      |         |               |
| tpydjournaltrans_interco_emp |          1 | idx_tpydjournaltrans_ie_EMPID          |            1 | EMP_ID          | A         |      125030 |     NULL | NULL   | YES  | BTREE      |         |               |
| tpydjournaltrans_interco_emp |          1 | idx_tpydjournaltrans_ie_taxtype        |            1 | tax_type        | A         |           4 |     NULL | NULL   | YES  | BTREE      |         |               |
| tpydjournaltrans_interco_emp |          1 | idx_tpydjournaltrans_ie_jobstatuscode  |            1 | jobstatuscode   | A         |          44 |     NULL | NULL   | YES  | BTREE      |         |               |
| tpydjournaltrans_interco_emp |          1 | idx_tpydjournaltrans_ie_BUSINESSUNIT2  |            1 | BUSINESS_UNIT   | A         |           6 |     NULL | NULL   | YES  | BTREE      |         |               |
| tpydjournaltrans_interco_emp |          1 | idx_tpydjournaltrans_ie_referencedate  |            1 | referencedate   | A         |          14 |     NULL | NULL   | YES  | BTREE      |         |               |
| tpydjournaltrans_interco_emp |          1 | idx_tpydjournaltrans_ie_journalcode    |            1 | journal_code    | A         |        4420 |     NULL | NULL   | YES  | BTREE      |         |               |
| tpydjournaltrans_interco_emp |          1 | idx_tpydjournaltrans_ie_reference_code |            1 | REFERENCE_CODE  | A         |          14 |     NULL | NULL   | YES  | BTREE      |         |               |
| tpydjournaltrans_interco_emp |          1 | idx_tpydjournaltrans_ie_BUSINESSUNIT   |            1 | REFERENCE_CODE  | A         |        4784 |     NULL | NULL   | YES  | BTREE      |         |               |
| tpydjournaltrans_interco_emp |          1 | idx_tpydjournaltrans_ie_BUSINESSUNIT   |            2 | BUSINESS_UNIT   | A         |       10370 |     NULL | NULL   | YES  | BTREE      |         |               |
| tpydjournaltrans_interco_emp |          1 | idx_tpydjournaltrans_ie_BUSINESSUNIT   |            3 | journal_code    | A         |       23922 |     NULL | NULL   | YES  | BTREE      |         |               |
+------------------------------+------------+----------------------------------------+--------------+-----------------+-----------+-------------+----------+--------+------+------------+---------+------

my question is
query on top is effective using composit index idx_tpydjournaltrans_ie_BUSINESSUNIT because on explain my query using this index ?

and if my query using composit index there is need more single column index or not ?