incrementing i with condition - sql

Question

I want to increment by i by 1 whenever the value is different for v_id.
i = 1;
for i in 1..10 loop
SELECT subject_details.NEXTVAL
INTO v_id
FROM dual;
INSERT INTO employee (id, subject)
VALUES (i,v_id);
i = i + 1;
end loop;
what this does is
id subject
1 3647
2 3647
3 5678
4 5678
5 5678
but what I want is to increment the value of "i" by 1 whenever there is a change in value for "v_id"
id subject
1 3647
1 3647
2 5678
2 5678
2 5678

Answer 1

I think you can just use dense_rank():
select t.*, dense_rank() over (order by subject)
from t;
If the values can be interleaved, then you can use lag() and a cumulative sum:
select t.*,
sum(case when prev_subject = subject then 0 else 1 end) over (order by id)
from (select t.*,
lag(subject) over (order by id) as prev_subject
from t
) t;

Answer 2

While there are good suggestions offered, I think they mostly miss your biggest mistake. I believe that is a miss understanding of pl/sql scoping rules. Somewhere in tour code (before what you posted) you defined a variable i then created i as the index variable of a FOR loop. The problem you face is that due to scoping rules these are not the same variable. According to documentation: (also see demonstration here)
for index name Name for the implicitly declared integer variable that is
local to the FOR LOOP statement. Statements outside the loop cannot
reference index. Statements inside the loop can reference index, but
cannot change its value. After the FOR LOOP statement runs, index is
undefined.
There are a couple other issues with you process:
In Oracle the assignment operator is := not =; (I assume this is just
a typo).
In each loop iteration you run "subject_details.NEXTVAL", and
subsequently insert that result into your table. Doing so will
increment the value every time. Thus you cannot produce your desired
output - nor your claimed output.

Answer 3

try
j = 1;
v_id_copy = 0;
for i in 1..10 loop
SELECT subject_details.NEXTVAL INTO v_id FROM dual;
if(v_id_copy==0) then
v_id_copy = v_id;
elseif (v_id_copy != v_id) then
j=j+1;
v_copy_id=v_id;
endif
insert into employee (id,subject) values (j,v_id)
end loop;