Пожалуйста, попробуйте это решение;
create table transactions (clientid INT PRIMARY KEY, date DATE, time TIME, CardNo INT, accountno VARCHAR(100), Transactiontype VARCHAR(20), curbalance float);
mysql> desc transactions;
+-----------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------------+--------------+------+-----+---------+-------+
| clientid | int(11) | NO | PRI | NULL | |
| date | date | YES | | NULL | |
| time | time | YES | | NULL | |
| CardNo | int(11) | YES | | NULL | |
| accountno | varchar(100) | YES | | NULL | |
| Transactiontype | varchar(20) | YES | | NULL | |
| curbalance | float | YES | | NULL | |
+-----------------+--------------+------+-----+---------+-------+
7 rows in set (0.00 sec)
mysql> insert into transactions values(1, '2019-02-26', '05:18:00', 865505, 'A6B55', 'withdraw', 20000);
mysql> insert into transactions values(2, '2019-02-26', '18:15:00', 865505, 'A6B55', 'deposit', 30000);
mysql> insert into transactions values(3, '2019-02-26', '21:10:00', 78805, '6979A', 'deposit', 100000);
mysql> select * from transactions;
+----------+------------+----------+--------+-----------+-----------------+------------+
| clientid | date | time | CardNo | accountno | Transactiontype | curbalance |
+----------+------------+----------+--------+-----------+-----------------+------------+
| 1 | 2019-02-26 | 05:18:00 | 865505 | A6B55 | withdraw | 20000 |
| 2 | 2019-02-26 | 18:15:00 | 865505 | A6B55 | deposit | 30000 |
| 3 | 2019-02-26 | 21:10:00 | 78805 | 6979A | deposit | 100000 |
+----------+------------+----------+--------+-----------+-----------------+------------+
mysql> select * from transactions where accountno = 'A6B55' ORDER BY time desc LIMIT 1;
+----------+------------+----------+--------+-----------+-----------------+------------+
| clientid | date | time | CardNo | accountno | Transactiontype | curbalance |
+----------+------------+----------+--------+-----------+-----------------+------------+
| 2 | 2019-02-26 | 18:15:00 | 865505 | A6B55 | deposit | 30000 |
+----------+------------+----------+--------+-----------+-----------------+------------+
Хорошего дня :) Ура ...