MySQL 5.5

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CREATE TABLE T
    (`id` varchar(6), `name` varchar(1), `create_time` datetime, `group_id` varchar(6));
    
INSERT INTO T
    (`id`, `name`, `create_time`, `group_id`)
VALUES
    ('1', 'a', '2022-01-01 12:00:00', 'group1'),
    ('2', 'b', '2022-01-01 13:00:00', 'group1'),
    ('3', 'c', '2022-01-01 12:00:00', NULL),
    ('4', 'd', '2022-01-01 13:00:00', NULL),
    ('5', 'e', NULL, 'group2'),
    ('6', 'f', '2022-01-03 13:33:00', 'group3'),
    ('7', 'f', '2022-01-04 14:44:00', 'group4'),
    ('8', 'g', null, 'group5'),
    ('9', 'h', '2022-01-05 15:55:00', 'group5');
-- ordering by coalesce(group_id, id)
select * from T t1
where coalesce(create_time, 0) = (
    select min(coalesce(create_time, 0)) from T t2
    where coalesce(t2.group_id, t2.id) = coalesce(t1.group_id, t1.id)
) and (
    select count(distinct coalesce(t2.group_id, t2.id)) from T t2
    where coalesce(t2.group_id, t2.id) <= coalesce(t1.group_id, t1.id)
) between 1 and 10
order by coalesce(t1.group_id, t1.id);


id
name
create_time
group_id


3
c
2022-01-01 12:00:00
null

4
d
2022-01-01 13:00:00
null

1
a
2022-01-01 12:00:00
group1

5
e
null
group2

6
f
2022-01-03 13:33:00
group3

7
f
2022-01-04 14:44:00
group4

8
g
null
group5


-- ordering and paginating by name
select *
from T t1
where coalesce(create_time, 0) = (
    select min(coalesce(create_time, 0)) from T t2
    where coalesce(t2.group_id, t2.id) = coalesce(t1.group_id, t1.id)
) and (
    select count(*) from (
        select * from T t1
        where coalesce(create_time, 0) = (
            select min(coalesce(create_time, 0)) from T t2
            where coalesce(t2.group_id, t2.id) = coalesce(t1.group_id, t1.id)
        )
    ) t3
    where t3.name < t1.name or
        t3.name = t1.name and coalesce(t3.group_id, t3.id) <= coalesce(t1.group_id, t1.id)
) between 1 and 5
order by t1.name;


id
name
create_time
group_id


1
a
2022-01-01 12:00:00
group1

3
c
2022-01-01 12:00:00
null

4
d
2022-01-01 13:00:00
null

5
e
null
group2

6
f
2022-01-03 13:33:00
group3

id	name	create_time	group_id
3	c	2022-01-01 12:00:00	null
4	d	2022-01-01 13:00:00	null
1	a	2022-01-01 12:00:00	group1
5	e	null	group2
6	f	2022-01-03 13:33:00	group3
7	f	2022-01-04 14:44:00	group4
8	g	null	group5