mysql - Find sum'd subset of data from larger data's group-by (subset being pre-grouping, reliant on grouping to determine)

Question

So I've got a problem that I am trying to solve purely in mySQL (I know it's a lot easier if I add in PHP, but I'm trying to avoid that for reasons outside the scope of this question). I have a query that combines a lot of tables/table data and returns the following relevant data (extra fields removed for my question):

Person	Day	Sales
A	1	6
B	1	5
A	2	7
C	2	6
A	3	5
B	3	5
C	3	5
D	3	5
A	4	7
B	4	5
A	5	7
D	5	5
A	6	6
B	6	5
C	6	6
D	6	5
A	7	5
B	7	5
C	7	5
D	7	6

question from:https://stackoverflow.com/questions/65911306/find-sumd-subset-of-data-from-larger-datas-group-by-subset-being-pre-grouping

Answer 1

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