MySQL 8.0

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create table  test (finish_position int, official_rating int, datec date )
insert into test values(11, null, '2013-09-18')
insert into test values(4, null, '2013-11-08')
insert into test values(3, null, '2014-02-27')
insert into test values(6, 65, '2014-04-24 ')
insert into test values(13, 63, '2014-05-05 ')
insert into test values(1, 59, '2014-07-04')
insert into test values(2, 65, '2014-08-04')
insert into test values(1, 60, '2015-07-14')
insert into test values(9, 60, '2015-08-04')
select finish_position, official_rating, datec, 0.00 as difference
from test
where datec <= (select min(datec) 
                from test 
                where finish_position = 1)


finish_position
official_rating
datec
difference


11
null
2013-09-18
0.00

4
null
2013-11-08
0.00

3
null
2014-02-27
0.00

6
65
2014-04-24
0.00

13
63
2014-05-05
0.00

1
59
2014-07-04
0.00


select finish_position, official_rating, datec, null as difference
from test
where datec > (select min(datec) 
                from test 
                where finish_position = 1)


finish_position
official_rating
datec
difference


2
65
2014-08-04
null

1
60
2015-07-14
null

9
60
2015-08-04
null


select finish_position,official_rating, datec
       , case when difference = 0.00 then difference
              else official_rating - lag(official_rating) over(order by datec) 
         end difference_1
from (
select finish_position, official_rating, datec, 0.00 as difference
from test
where datec <= (select min(datec) 
                from test 
                where finish_position = 1)
union 
select finish_position, official_rating, datec, null as difference
from test
where datec > (select min(datec) 
                from test 
                where finish_position = 1)) t1
order by datec;


finish_position
official_rating
datec
difference_1


11
null
2013-09-18
0.00

4
null
2013-11-08
0.00

3
null
2014-02-27
0.00

6
65
2014-04-24
0.00

13
63
2014-05-05
0.00

1
59
2014-07-04
0.00

2
65
2014-08-04
6.00

1
60
2015-07-14
-5.00

9
60
2015-08-04
0.00

finish_position	official_rating	datec
11	null	2013-09-18
4	null	2013-11-08
3	null	2014-02-27
6	65	2014-04-24
13	63	2014-05-05
1	59	2014-07-04