SQLite 3.39

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CREATE TABLE T_A (year_A INT, amount_A DOUBLE);
✓
INSERT INTO T_A (`year_A`, `amount_A`) VALUES
  ('2020', '100.0'),
  ('2020', '200.0'),
  ('2021', '300.0'), ('2021', '400.0');
✓
CREATE TABLE T_B (year_B INT, amount_B DOUBLE);
✓
INSERT INTO T_B (`year_B`, `amount_B`) VALUES
  ('2021', '1000.0'),
  ('2021', '2000.0'),
  ('2022', '3000.0'), ('2022', '4000.0');
✓
WITH 
  cte_A AS (SELECT year_A, SUM(amount_A) AS sum_A FROM T_A GROUP BY year_A),
  cte_B AS (SELECT year_B, SUM(amount_B) AS sum_B FROM T_B GROUP BY year_B)
SELECT COALESCE(a.year_A, b.year_B) year,
       COALESCE(a.sum_A, 0) AS sum_A,
       COALESCE(b.sum_B, 0) AS sum_B
FROM cte_A AS a FULL OUTER JOIN cte_B AS b
ON b.year_B = a.year_A
ORDER BY year;


year
sum_A
sum_B


2020
300
0

2021
700
3000

2022
0
7000


WITH cte AS (
  SELECT year_A AS year, amount_A, 0 AS amount_B FROM T_A
  UNION ALL
  SELECT year_B, 0, amount_B FROM T_B
)
SELECT year,
       SUM(amount_A) AS sum_A,
       SUM(amount_B) AS sum_B
FROM cte
GROUP BY year
ORDER BY year;


year
sum_A
sum_B


2020
300
0

2021
700
3000

2022
0
7000