MySQL 8.0

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create table tab1 (form_unique_identifier varchar(10), field_number int, field_label varchar(20), total_drop_off int, total_visitors int);
insert into tab1 values('FA11567953', 0, 'Name', 4, 100),
('FA11567953', 1, 'Dropdown', 5, 100),
('FA11567953', 3, 'File', 32, 100),
('FA11567953', 4, 'Multi select field', 10, 100),
('FA45345345', 0, 'Name', 1, 233),
('FA45345345', 11, 'Dropdown', 7, 233),
('FA45345345', 31, 'File', 2, 233),
('FA45345345', 44, 'Multi select field', 3, 233);
select * from tab1;


form_unique_identifier
field_number
field_label
total_drop_off
total_visitors


FA11567953
0
Name
4
100

FA11567953
1
Dropdown
5
100

FA11567953
3
File
32
100

FA11567953
4
Multi select field
10
100

FA45345345
0
Name
1
233

FA45345345
11
Dropdown
7
233

FA45345345
31
File
2
233

FA45345345
44
Multi select field
3
233


select *, total_visitors - ifnull(sum(total_drop_off) over(partition by (form_unique_identifier) order by field_number ROWS BETWEEN UNBOUNDED PRECEDING AND 1 PRECEDING),0) totals
from tab1
group by form_unique_identifier, field_number, field_label, total_drop_off, total_visitors
order by form_unique_identifier;


form_unique_identifier
field_number
field_label
total_drop_off
total_visitors
totals


FA11567953
0
Name
4
100
100

FA11567953
1
Dropdown
5
100
96

FA11567953
3
File
32
100
91

FA11567953
4
Multi select field
10
100
59

FA45345345
0
Name
1
233
233

FA45345345
11
Dropdown
7
233
232

FA45345345
31
File
2
233
225

FA45345345
44
Multi select field
3
233
223

form_unique_identifier	field_number	field_label	total_drop_off	total_visitors
FA11567953	0	Name	4	100
FA11567953	1	Dropdown	5	100
FA11567953	3	File	32	100
FA11567953	4	Multi select field	10	100
FA45345345	0	Name	1	233
FA45345345	11	Dropdown	7	233
FA45345345	31	File	2	233
FA45345345	44	Multi select field	3	233