SQLite 3.27

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CREATE TABLE tablename (`Category` VARCHAR(4), `Price` INTEGER, `Date` TEXT);

✓
INSERT INTO tablename (`Category`, `Price`, `Date`) VALUES
  ('Cat1', '20', '2019-04'),
  ('Cat2', '12', '2019-04'),
  ('Cat3', '5', '2019-04'),
  ('Cat1', '23', '2020-04'),
  ('Cat2', '17', '2020-04'),
  ('Cat3', '8', '2020-04');
✓
SELECT Category,
       ROUND(1.0 * next_price / Price - 1, 2) Pct_change,
       SUBSTR(Date, 1, 4) || '-' || SUBSTR(next_date, 1, 4) Period
FROM (
  SELECT *,
         LEAD(Price) OVER (PARTITION BY Category ORDER BY Date) next_price,
         LEAD(Date) OVER (PARTITION BY Category ORDER BY Date) next_date
  FROM tablename
)
WHERE next_date IS NOT NULL


Category
Pct_change
Period


Cat1
0.15
2019-2020

Cat2
0.42
2019-2020

Cat3
0.6
2019-2020