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(12, 68, '2014-10-28')
insert into test values(9, 62, '2014-12-09')
insert into test values(5, 65, '2015-01-08')
insert into test values(7, 60, '2015-01-29')
insert into test values(11, 65, '2015-04-08')
insert into test values(5, 63, '2015-04-22')
insert into test values(1, 60, '2015-07-14')
insert into test values(9, 60, '2015-08-04')
insert into test values(8, 56, '2016-01-22')
insert into test values(4, 52, '2016-02-26')
insert into test values(7, 50, '2016-03-31')
insert into test values(8, 48, '2016-04-25')
insert into test values(4, 56, '2016-07-12')
insert into test values(8, 47, '2016-09-23')
insert into test values(9, 52, '2017-06-20')
insert into test values(1, 50, '2017-07-04')
insert into test values(3, 55, '2017-07-20')
insert into test values(3, 48, '2017-07-29')
select finish_position,official_rating, datec
       , case when finish_position = 1 then 0.00
	      when t1.datec >= (select tt.datec 
                                from test tt
                                where DATEDIFF(tt.datec, t1.datec) in 
                                  (select max(datediff(ttt.datec, t1.datec))
                                   from test ttt
                                   where finish_position = 1
                                   and ttt.datec <= t1.datec)) 
              then (select t.official_rating 
                    from test t
                    where datediff(t.datec, t1.datec) in (select max(datediff(ttt.datec, t1.datec))
                    from test ttt
                    where finish_position = 1
                    and ttt.datec <= t1.datec)) - t1.official_rating
              end difference
from (
select finish_position, official_rating, datec
       , case when finish_position = 1 then null
              else 0.00 
         end 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


11
null
2013-09-18
null

4
null
2013-11-08
null

3
null
2014-02-27
null

6
65
2014-04-24
null

13
63
2014-05-05
null

1
59
2014-07-04
0.00

2
65
2014-08-04
-6

12
68
2014-10-28
-9

9
62
2014-12-09
-3

5
65
2015-01-08
-6

7
60
2015-01-29
-1

11
65
2015-04-08
-6

5
63
2015-04-22
-4

1
60
2015-07-14
0.00

9
60
2015-08-04
0

8
56
2016-01-22
4

4
52
2016-02-26
8

7
50
2016-03-31
10

8
48
2016-04-25
12

4
56
2016-07-12
4

8
47
2016-09-23
13

9
52
2017-06-20
8

1
50
2017-07-04
0.00

3
55
2017-07-20
-5

3
48
2017-07-29
2

finish_position	official_rating	datec	difference
11	null	2013-09-18	null
4	null	2013-11-08	null
3	null	2014-02-27	null
6	65	2014-04-24	null
13	63	2014-05-05	null
1	59	2014-07-04	0.00
2	65	2014-08-04	-6
12	68	2014-10-28	-9
9	62	2014-12-09	-3
5	65	2015-01-08	-6
7	60	2015-01-29	-1
11	65	2015-04-08	-6
5	63	2015-04-22	-4
1	60	2015-07-14	0.00
9	60	2015-08-04	0
8	56	2016-01-22	4
4	52	2016-02-26	8
7	50	2016-03-31	10
8	48	2016-04-25	12
4	56	2016-07-12	4
8	47	2016-09-23	13
9	52	2017-06-20	8
1	50	2017-07-04	0.00
3	55	2017-07-20	-5
3	48	2017-07-29	2