Puoi ottenerlo con un cte ricorsivo come questo:
with RECURSIVE ctetest as (SELECT * FROM (values ('2020-12-31'::date,'Alex',35,100,'A+'),
('2021-01-31'::date,'Alex',35,110,'A'),
('2021-05-31'::date,'Alex',35,999,'A+'),
('2021-06-30'::date,'Jhon',20,175,'B-'),
('2021-09-30'::date,'Jhon',20,200,'B+')) v (mth, emp, age, salary, rating)),
cte AS (
SELECT MIN(mth) AS mth, emp, age, salary, rating
FROM ctetest
GROUP BY emp, age, salary, rating
UNION
SELECT COALESCE(n.mth, (l.mth + interval '1 day' + interval '1 month' - interval '1 day')::date), COALESCE(n.emp, l.emp),
COALESCE(n.age, l.age), COALESCE(n.salary, l.salary), COALESCE(n.rating, l.rating)
FROM cte l
LEFT OUTER JOIN ctetest n ON n.mth = (l.mth + interval '1 day' + interval '1 month' - interval '1 day')::date
AND n.emp = l.emp
WHERE (l.mth + interval '1 day' + interval '1 month' - interval '1 day')::date <= (SELECT MAX(mth) FROM ctetest)
)
SELECT * FROM cte order by 2, 1;
Nota che sebbene ctetest non sia esso stesso recursive , essendo utilizzato solo per ottenere i dati del test, se qualsiasi cte tra più ctes è recursive , devi avere la parola chiave ricorsiva dopo with .
