Cheking if an entry exists in another table using cursor - sql

Question

My task is to insert entries from one table to another by using parametrized cursor. Here's what I have tried
DECLARE
oldroll NUMBER;
newroll NUMBER;
oldname VARCHAR2(25);
newname VARCHAR2(25);
CURSOR c_orollcall (roll_no NUMBER,name VARCHAR2) IS SELECT * FROM o_rollcall;
PROCEDURE procedure_2;
PROCEDURE procedure_2 AS
BEGIN
OPEN c_orollcall;
LOOP
FETCH c_orollcall INTO oldroll ,oldname;
SET #count = 0;
SELECT roll_no INTO #count FROM n_rollcall WHERE EXISTS (oldroll);
IF #count>0 THEN
DBMS_OUTPUT.PUT_LINE('ENTRY ALREADY EXISTS');
ELSE
INSERT INTO n_rollcall VALUES (oldroll,oldname);
END IF;
EXIT WHEN c_orollcall%NOTFOUND;
END LOOP;
CLOSE c_orollcall;
END;
/
BEGIN
procedure_2;
END
/
I am getting a bunch of errors and dont' understand how to proceed further.I previously posted a question about this too but it generated more errors .
here's the problem statement:
Write a PL/SQL block of code using parameterized Cursor that will merge the data available in
the newly created table N_RollCall with the data available in the table O_RollCall. If the data in
the first table already exist in the second table then that data should be skipped.

Answer 1

I would suggest you to use an extra variable to store the result and check it in IF codition
SET count = 0;
SELECT COUNT(roll_no) INTO count FROM n_rollcall WHERE EXISTS (oldroll);
Updated code:
CREATE OR REPLACE PROCEDURE procedure_2 AS
DECLARE count INT default 0;
BEGIN
OPEN c_orollcall;
LOOP
FETCH c_orollcall INTO oldroll ,oldname;
SET count = 0;
SELECT roll_no INTO count FROM n_rollcall WHERE EXISTS (oldroll);
IF count>0 THEN
DBMS_OUTPUT.PUT_LINE('ENTRY ALREADY EXISTS');
ELSE
INSERT INTO n_rollcall VALUES (oldroll,oldname);
END IF;
EXIT WHEN c_orollcall%NOTFOUND;
END LOOP;
CLOSE c_orollcall;
END;
/