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Help with an interesting Postgres question: Why isn't an Index Only Scan used on a partition accessed via the parent table?.
create table t as
select v.*
from (values (1, 10, 20, 100, 30),
(2, 20, 40, 200, 60),
(3, 30, 60, 0 , 260),
(4, 40, 70, 0 , 200),
(5, 50, 80, 50 , 130)
) v(Row, Col1, Col2, Col3, Result)
5 rows affected
select t.*,
(case when col3 <> 0 then col1 + col2
else sum(col2 + col3) over (partition by grp order by row desc)
end) as result
from (select t.*,
sum(case when col3 <> 0 then 1 else 0 end) over (order by row desc) as grp
from t
) t
order by row
| row | col1 | col2 | col3 | result | grp | result |
|---|---|---|---|---|---|---|
| 1 | 10 | 20 | 100 | 30 | 3 | 30 |
| 2 | 20 | 40 | 200 | 60 | 2 | 60 |
| 3 | 30 | 60 | 0 | 260 | 1 | 260 |
| 4 | 40 | 70 | 0 | 200 | 1 | 200 |
| 5 | 50 | 80 | 50 | 130 | 1 | 130 |