MIN,MAX value on windowed data

DROP TABLE IF EXISTS tbl_trans;
CREATE TABLE IF NOT EXISTS tbl_trans(
    transactions VARCHAR(10),
    history DATETIME,
    PRIMARY KEY (transactions,history)
) ENGINE=MyISAM CHARSET utf8;

INSERT INTO tbl_trans
VALUES
('TRANS-A','2017-08-30 08:00:00'),
('TRANS-A','2017-08-30 08:10:00'),
('TRANS-A','2017-08-30 08:20:00'),
('TRANS-A','2017-08-30 08:30:00'),
('TRANS-A','2017-08-30 08:40:00'),
('TRANS-A','2017-08-30 08:50:00'),
('TRANS-A','2017-08-30 09:00:00'),
('TRANS-B','2017-08-30 09:10:00'),
('TRANS-B','2017-08-30 09:20:00'),
('TRANS-B','2017-08-30 09:30:00'),
('TRANS-B','2017-08-30 09:40:00'),
('TRANS-B','2017-08-30 09:50:00'),
('TRANS-A','2017-08-30 10:00:00'),
('TRANS-A','2017-08-30 10:10:00'),
('TRANS-A','2017-08-30 10:20:00'),
('TRANS-A','2017-08-30 10:30:00'),
('TRANS-A','2017-08-30 10:40:00'),
('TRANS-C','2017-08-30 10:50:00'),
('TRANS-C','2017-08-30 11:00:00'),
('TRANS-C','2017-08-30 11:10:00'),
('TRANS-C','2017-08-30 11:20:00'),
('TRANS-A','2017-08-30 11:30:00'),
('TRANS-A','2017-08-30 11:40:00'),
('TRANS-C','2017-08-30 11:50:00'),
('TRANS-C','2017-08-30 12:00:00'),
('TRANS-B','2017-08-30 12:10:00'),
('TRANS-A','2017-08-30 12:20:00'),
('TRANS-A','2017-08-30 12:30:00'),
('TRANS-A','2017-08-30 12:40:00'),
('TRANS-A','2017-08-30 12:50:00');

SELECT * FROM tbl_trans;
+--------------+---------------------+
| transactions | history             |
+--------------+---------------------+
| TRANS-A      | 2017-08-30 08:00:00 |
| TRANS-A      | 2017-08-30 08:10:00 |
| TRANS-A      | 2017-08-30 08:20:00 |
| TRANS-A      | 2017-08-30 08:30:00 |
| TRANS-A      | 2017-08-30 08:40:00 |
| TRANS-A      | 2017-08-30 08:50:00 |
| TRANS-A      | 2017-08-30 09:00:00 |
| TRANS-A      | 2017-08-30 10:00:00 |
| TRANS-A      | 2017-08-30 10:10:00 |
| TRANS-A      | 2017-08-30 10:20:00 |
| TRANS-A      | 2017-08-30 10:30:00 |
| TRANS-A      | 2017-08-30 10:40:00 |
| TRANS-A      | 2017-08-30 11:30:00 |
| TRANS-A      | 2017-08-30 11:40:00 |
| TRANS-A      | 2017-08-30 12:20:00 |
| TRANS-A      | 2017-08-30 12:30:00 |
| TRANS-A      | 2017-08-30 12:40:00 |
| TRANS-A      | 2017-08-30 12:50:00 |
| TRANS-B      | 2017-08-30 09:10:00 |
| TRANS-B      | 2017-08-30 09:20:00 |
| TRANS-B      | 2017-08-30 09:30:00 |
| TRANS-B      | 2017-08-30 09:40:00 |
| TRANS-B      | 2017-08-30 09:50:00 |
| TRANS-B      | 2017-08-30 12:10:00 |
| TRANS-C      | 2017-08-30 10:50:00 |
| TRANS-C      | 2017-08-30 11:00:00 |
| TRANS-C      | 2017-08-30 11:10:00 |
| TRANS-C      | 2017-08-30 11:20:00 |
| TRANS-C      | 2017-08-30 11:50:00 |
| TRANS-C      | 2017-08-30 12:00:00 |
+--------------+---------------------+

-- query untuk pengelompokan data berdasarkan `transactions` dalam urutan `history`
SELECT
     IF(transactions!=@prev,@num:=@num+1,@num) AS grup,
     @prev:=transactions AS transactions,
     history
FROM tbl_trans
     JOIN (SELECT @prev:=0,@num:=0) init
ORDER BY history;

+------+--------------+---------------------+
| grup | transactions | history             |
+------+--------------+---------------------+
|    1 | TRANS-A      | 2017-08-30 08:00:00 |
|    1 | TRANS-A      | 2017-08-30 08:10:00 |
|    1 | TRANS-A      | 2017-08-30 08:20:00 |
|    1 | TRANS-A      | 2017-08-30 08:30:00 |
|    1 | TRANS-A      | 2017-08-30 08:40:00 |
|    1 | TRANS-A      | 2017-08-30 08:50:00 |
|    1 | TRANS-A      | 2017-08-30 09:00:00 |
|    2 | TRANS-B      | 2017-08-30 09:10:00 |
|    2 | TRANS-B      | 2017-08-30 09:20:00 |
|    2 | TRANS-B      | 2017-08-30 09:30:00 |
|    2 | TRANS-B      | 2017-08-30 09:40:00 |
|    2 | TRANS-B      | 2017-08-30 09:50:00 |
|    3 | TRANS-A      | 2017-08-30 10:00:00 |
|    3 | TRANS-A      | 2017-08-30 10:10:00 |
|    3 | TRANS-A      | 2017-08-30 10:20:00 |
|    3 | TRANS-A      | 2017-08-30 10:30:00 |
|    3 | TRANS-A      | 2017-08-30 10:40:00 |
|    4 | TRANS-C      | 2017-08-30 10:50:00 |
|    4 | TRANS-C      | 2017-08-30 11:00:00 |
|    4 | TRANS-C      | 2017-08-30 11:10:00 |
|    4 | TRANS-C      | 2017-08-30 11:20:00 |
|    5 | TRANS-A      | 2017-08-30 11:30:00 |
|    5 | TRANS-A      | 2017-08-30 11:40:00 |
|    6 | TRANS-C      | 2017-08-30 11:50:00 |
|    6 | TRANS-C      | 2017-08-30 12:00:00 |
|    7 | TRANS-B      | 2017-08-30 12:10:00 |
|    8 | TRANS-A      | 2017-08-30 12:20:00 |
|    8 | TRANS-A      | 2017-08-30 12:30:00 |
|    8 | TRANS-A      | 2017-08-30 12:40:00 |
|    8 | TRANS-A      | 2017-08-30 12:50:00 |
+------+--------------+---------------------+

-- query untuk mendapatkan nilai MIN() dan MAX() dari data yg sudah dibuat grup-nya
SELECT
    transactions,
    MIN(history) AS startdate,
    MAX(history) AS enddate
FROM
    (
    SELECT
        IF(transactions!=@prev,@grup:=@grup+1,@grup) AS grup,
        @prev:=transactions AS transactions,
        history
    FROM tbl_trans
        JOIN (SELECT @prev:=0,@grup:=0) init
    ORDER BY history
    )
    AS a_table
GROUP BY grup
ORDER BY grup,history;

+--------------+---------------------+---------------------+
| transactions | startdate           | enddate             |
+--------------+---------------------+---------------------+
| TRANS-A      | 2017-08-30 08:00:00 | 2017-08-30 09:00:00 |
| TRANS-B      | 2017-08-30 09:10:00 | 2017-08-30 09:50:00 |
| TRANS-A      | 2017-08-30 10:00:00 | 2017-08-30 10:40:00 |
| TRANS-C      | 2017-08-30 10:50:00 | 2017-08-30 11:20:00 |
| TRANS-A      | 2017-08-30 11:30:00 | 2017-08-30 11:40:00 |
| TRANS-C      | 2017-08-30 11:50:00 | 2017-08-30 12:00:00 |
| TRANS-B      | 2017-08-30 12:10:00 | 2017-08-30 12:10:00 |
| TRANS-A      | 2017-08-30 12:20:00 | 2017-08-30 12:50:00 |
+--------------+---------------------+---------------------+