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, weeks, MAX(total_sales) total_sales
FROM (
  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) total_sales
  FROM table1
  GROUP BY item, weeks
)
GROUP BY weeks;


item
weeks
total_sales


cupcake
1-2
45

cookie
3-4
34

cookie
5
120

cupcake
>5
42