Get two records from PLSQL cursor - plsql

Question

My question is short. I create a cursor to get some values from my table. I want to get the current record of cursor (the fetched record) and the next record from the cursor without fetching it, because I want to make a calculation over the current record and the next record. In traditional programming it's a simple operation; you can do it with a for index by increasing it by 1.
Do you have any suggestions?

Answer 1

I want to make a calculation over the
current record and the next record.
Presuming you are using Oracle, this can be done quite simply in SQL using analtyical functions, specifically the lead() function. This retrieves a column's value from the next nth record (default n=1).
SQL> select empno
2 , sal as this_sal
3 , lead(sal) over (order by empno) as next_sal
4 from emp
5 order by empno
6 /
EMPNO THIS_SAL NEXT_SAL
---------- ---------- ----------
7369 800 1600
7499 1600 1250
7521 1250 2975
7566 2975 1250
7654 1250 2850
7698 2850 2450
....
This query can be using in a cursor or any other mechanism for retrieving records.

Answer 2

I'm not sure you can do that without moving the cursor, but you should be able to accomplish the same goal like this (psuedocode):
open cursor;
fetch cursor to rec1;
if cursor%found then
loop
fetch cursor to rec2;
exit when cursor%notfound;
perform calculations with rec1 and rec2;
rec1 := rec2;
end loop;
end if;

Answer 3

To answer you specific question, you could use BULK COLLECT and its limit clause into a collection (table) variable.
DECLARE
CURSOR my_cursor IS
[YOUR SQL HERE];
TYPE t_my_type IS TABLE OF my_cursor%ROWTYPE INDEX BY BINARY_INTEGER;
v_my_var t_my_type;
BEGIN
FETCH my_cursor BULK COLLECT INTO v_my_var LIMIT 2;
dbms_output.put_line('My first value: ' || v_my_var(1).some_column);
dbms_output.put_line('My second value: ' || v_my_var(2).some_column);
END;
The limit clause will cause only the first two records to be fetched and stored. The first record will have an index of 1 and the second will be 2.

Answer 4

You can compare two variables by saving one into local and then compare it with cursor value for example
declare
l_local1 table_name%type := null;
begin
for c1 in (select
*
from
table_name
where some clause)
loop
-- do comparation
if l_local1 is not null and c1.field_value is not null then
-- do something to compare
.
.
.
-- empty local1 variable
l_local1 := null;
end if;
-- get the value of loop in local variable
l_local1 := c1.field_value;
end loop;
end;