MySQL 8.0

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CREATE TABLE IF NOT EXISTS example(BatchNum int, Time DATETIME);
INSERT INTO example 
VALUES(1,'2020-12-04 05:06:12'), (1,'2020-12-04 05:06:13'), (1,'2020-12-04 05:06:14'), (2,'2020-12-04 05:06:20'), (2,'2020-12-04 05:07:12'), (2,'2020-12-04 05:07:20'), (1,'2020-12-04 05:07:25'), (1,'2020-12-04 05:07:35'), (3,'2020-12-04 05:07:35');
select *
from (
    select e.*,
        lag(batchnum) over(order by time) lag_batchnum
    from example e
) e
where not lag_batchnum <=> batchnum


BatchNum
Time
lag_batchnum


1
2020-12-04 05:06:12
null

2
2020-12-04 05:06:20
1

1
2020-12-04 05:07:25
2

3
2020-12-04 05:07:35
1


select e.*
from example e
where not batchnum <=> (
	select e1.batchnum
	from example e1
	where e1.time < e.time
	order by e1.time desc
	limit 1
)


BatchNum
Time


1
2020-12-04 05:06:12

2
2020-12-04 05:06:20

1
2020-12-04 05:07:25

3
2020-12-04 05:07:35

BatchNum	Time	lag_batchnum
1	2020-12-04 05:06:12	null
2	2020-12-04 05:06:20	1
1	2020-12-04 05:07:25	2
3	2020-12-04 05:07:35	1