SQLite 3.27

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CREATE TABLE table1 (`item` TEXT, `week` INTEGER, `sales` INTEGER);
insert into table1 values
('ice cream', 1, 17),
('cupcake', 1, 25),
('cookie', 1, 22),
('ice cream', 2, 20),
('cupcake', 2, 20),
('cookie', 2, 2),
('ice cream', 3, 17),
('cupcake', 3, 9),
('cookie', 3, 10),
('ice cream', 4, 10),
('cupcake', 4, 7),
('cookie', 4, 24),
('ice cream', 5, 12),
('cupcake', 5, 4),
('cookie', 5, 120),
('ice cream', 6, 13),
('cupcake', 6, 16),
('cookie', 6, 10),     
('ice cream', 7, 2),
('cupcake', 7, 10),
('cookie', 7, 9), 
('ice cream', 8, 25),
('cupcake', 8, 16),
('cookie', 8, 21);
SELECT item,
       CASE 
         WHEN week <= 2 THEN '1-2'
         WHEN week <= 4 THEN '3-4'
         WHEN week <= 5 THEN '5'
         ELSE '>5'
       END weeks,
       SUM(sales) OVER(partition by week order by item) as total_sales
FROM table1
GROUP BY item;


item
weeks
total_sales


cookie
1-2
22

cupcake
1-2
47

ice cream
1-2
64