MariaDB 10.3

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create table dividends( id bigint unsigned auto_increment primary key,
                        company varchar(5) not null,
                        record_date date null,
                        summ integer null );
INSERT INTO dividends (company, record_date, summ) VALUES 
('CompA','19-12-20','192'),
('CompA','19-07-09','155'),
('CompA','18-12-21','95'),
('CompA','18-07-11','130'),
('CompA','17-12-22','85'),
('CompA','17-07-10','120'),
('CompA','16-12-23','75'),
('CompA','16-07-12','112'),
('CompA','15-12-24','65'),
('CompA','15-07-14','94'),
('CompA','14-12-26','60'),
('CompA','14-07-15','60'),
('CompA','13-08-15','50'),
('CompA','13-01-13','50'),
('CompA','12-11-12','40'),
('CompA','12-01-11','75'),
('CompB','19-01-11','75'),
('CompB','18-01-11','25'),
('CompB','17-01-11','75'),
('CompB','16-01-11','60'),
('CompB','15-01-11','55'),
('CompB','14-01-11','45'),
('CompB','13-01-11','35'),
('CompB','12-01-11','25'),
('CompC','19-02-21','75'),
('CompC','18-03-12','70'),
('CompC','14-06-01','40'),
('CompC','13-07-22','20');
SELECT * FROM dividends;

id	company	record_date	summ
1	CompA	2019-12-20	192
2	CompA	2019-07-09	155
3	CompA	2018-12-21	95
4	CompA	2018-07-11	130
5	CompA	2017-12-22	85
6	CompA	2017-07-10	120
7	CompA	2016-12-23	75
8	CompA	2016-07-12	112
9	CompA	2015-12-24	65
10	CompA	2015-07-14	94
11	CompA	2014-12-26	60
12	CompA	2014-07-15	60
13	CompA	2013-08-15	50
14	CompA	2013-01-13	50
15	CompA	2012-11-12	40
16	CompA	2012-01-11	75
17	CompB	2019-01-11	75
18	CompB	2018-01-11	25
19	CompB	2017-01-11	75
20	CompB	2016-01-11	60
21	CompB	2015-01-11	55
22	CompB	2014-01-11	45
23	CompB	2013-01-11	35
24	CompB	2012-01-11	25
25	CompC	2019-02-21	75
26	CompC	2018-03-12	70
27	CompC	2014-06-01	40
28	CompC	2013-07-22	20

WITH
cte1 AS ( SELECT company, 
                 YEAR(record_date) record_year, 
                 SUM(summ) summ
          FROM dividends
          GROUP BY 1, 2 ),
cte2 AS ( SELECT company, 
                 record_year, 
                 summ, 
                 LAG(summ) OVER (PARTITION BY company ORDER BY record_year) lag_summ, 
                 LAG(record_year) OVER (PARTITION BY company ORDER BY record_year) lag_year,
                 (summ < COALESCE(LAG(summ) OVER (PARTITION BY company ORDER BY record_year), 0)) summ_not_over,
                 (COALESCE(LEAD(record_year) OVER (PARTITION BY company ORDER BY record_year), YEAR(CURRENT_DATE)) - record_year) != 1 is_not_consecutive
          FROM cte1 ),
cte3 AS ( SELECT company, 
                 record_year, 
                 summ,
                 SUM(summ_not_over) OVER (PARTITION BY company ORDER BY record_year DESC) summ_over,
                 SUM(is_not_consecutive) OVER (PARTITION BY company ORDER BY record_year DESC) is_consecutive
          FROM cte2
          WHERE record_year >= YEAR(CURRENT_DATE) - 7 )
SELECT company, (SUM(!is_consecutive) + SUM(!(summ_over + is_consecutive))) / 14 DSI
FROM cte3
GROUP BY 1;

company	DSI
CompA	0.9286
CompB	0.5714
CompC	0.2857