Iterate in oracle using incremental iterable variables - oracle

Question

I'm trying to get some data iteratively from an Oracle database. Here's a skeleton of the query I'm trying:
select a.id, a.cd,
sum(case
when b.count>0
then b.count+1
when b.count=0
then 1
else 0
end),
sum(case
when b.count>0 and b.received is NULL and c.rid is NULL
then b.count+1
when b.count=0 and b.received is NULL and c.rid is NULL\
then 1
else 0
end),
sum(case
when c.err='Y'
then 1
else 0
end),
max(b.sent)
from
b
left join c
on b.oid=c.oid
inner join a
on b.id=a.id
inner join d
on (d.oid=b.oid
and d.tss=
(select max(tss)
from e where rid=b.rid
and rcd=b.rcd))
where b.sent is not null
/* !!! The line below !!! */
and b.sent > sysdate -2*i/24 and b.sent <= sysdate -2*(i-1)/24
and b.id=7
group by a.id,a.cd
order by a.id
Please notice the highlighted part and b.sent > sysdate -2*i/24 and b.sent <= sysdate -2*(i-1)/24. This is where I want to iterate incrementing the value of i each time. I tried putting this in a for loop incrementing the value of i each time but got the error
"PLS-00428: an INTO clause is expected in this SELECT statement".
When I tried to declare variables and put the results of the select statement into them, I was unable to due to the group by statements. I'm getting stuck at this point hence reaching out to the members for the expert help. Thank you for patiently going through this. Please do let me know if there is a way to resolve this issue.

Answer 1

You do not need an explicit loop if you just want to execute some query for subsequent values of parameter. You can generate a sequence of values and use lateral join (in Oracle 12+) for each row:
create table t
as
select level as l
, sysdate + trunc(level / 5) as v
from dual
connect by level < 13
with a as (
select level as i
from dual
connect by level < 6
)
select
a.i as iter,
t2.*
from a
outer apply (
select *
from t
where v between sysdate - i
and sysdate + i
) t2
ITER | L | V
---: | -: | :--------
1 | 1 | 19-APR-21
1 | 2 | 19-APR-21
1 | 3 | 19-APR-21
1 | 4 | 19-APR-21
1 | 5 | 20-APR-21
1 | 6 | 20-APR-21
1 | 7 | 20-APR-21
1 | 8 | 20-APR-21
1 | 9 | 20-APR-21
2 | 1 | 19-APR-21
2 | 2 | 19-APR-21
2 | 3 | 19-APR-21
2 | 4 | 19-APR-21
2 | 5 | 20-APR-21
2 | 6 | 20-APR-21
2 | 7 | 20-APR-21
2 | 8 | 20-APR-21
2 | 9 | 20-APR-21
2 | 10 | 21-APR-21
2 | 11 | 21-APR-21
2 | 12 | 21-APR-21
3 | 1 | 19-APR-21
3 | 2 | 19-APR-21
3 | 3 | 19-APR-21
3 | 4 | 19-APR-21
3 | 5 | 20-APR-21
3 | 6 | 20-APR-21
3 | 7 | 20-APR-21
3 | 8 | 20-APR-21
3 | 9 | 20-APR-21
3 | 10 | 21-APR-21
3 | 11 | 21-APR-21
3 | 12 | 21-APR-21
4 | 1 | 19-APR-21
4 | 2 | 19-APR-21
4 | 3 | 19-APR-21
4 | 4 | 19-APR-21
4 | 5 | 20-APR-21
4 | 6 | 20-APR-21
4 | 7 | 20-APR-21
4 | 8 | 20-APR-21
4 | 9 | 20-APR-21
4 | 10 | 21-APR-21
4 | 11 | 21-APR-21
4 | 12 | 21-APR-21
5 | 1 | 19-APR-21
5 | 2 | 19-APR-21
5 | 3 | 19-APR-21
5 | 4 | 19-APR-21
5 | 5 | 20-APR-21
5 | 6 | 20-APR-21
5 | 7 | 20-APR-21
5 | 8 | 20-APR-21
5 | 9 | 20-APR-21
5 | 10 | 21-APR-21
5 | 11 | 21-APR-21
5 | 12 | 21-APR-21
db<>fiddle here