Oracle 18c

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CREATE TABLE tablename ("id" int, "key" int, "date" date);
INSERT INTO tablename VALUES (0, 1, date '2020-01-01');
1 rows affected

INSERT INTO tablename VALUES (1, 1, date '2021-01-01');
1 rows affected

SELECT t.*
FROM (
  SELECT t.*, LEAD(t."date") OVER (PARTITION BY t."key" ORDER BY t."date") NEXT_DATE
  FROM tablename t
  WHERE t."key" = 1
) t
WHERE t."date" = date '2020-01-01'


id
key
date
NEXT_DATE


0
1
01-JAN-20
01-JAN-21