PL/SQL cursor with IF condition - sql

Question

I Have below cursor in the code.
CURSOR cur1
IS
SELECT a, b, c, d,
FROM EMP;
BEGIN
--Stored procedure logic
END
This curosr is getting information from EMP table.
But I need to change is as per below
There is a table (Table1) with Key Value pairs.
If the Table1 value is TRUE then the cursor should be created with STUDENT table
If the table1 value is FALSE then the cursor should be created with EMP table.
I can check the Value in the Table1 as below
select t.value into variable1 from Table1 t where s.key='xxxxx';
And I want write something like
IF variable1 := 'true'
curosr created with STUDENT
ELSE
curosr created with EMP
END IF
BEGIN
--Stored procedure logic
END
How to do it?

Answer 1

In another way you can just keep two CURSORS for those two scenarios and OPEN them on the condition. Declaring two CURSORS will not affect to the performance; you should be careful when OPEN a CURSOR and FETCHING from it.
PROCEDURE Get_Details_On_Condition ( name_ OUT VARCHAR2, isEmp IN BOOLEAN )
IS
CURSOR get_emp IS
SELECT name
FROM EMP;
CURSOR get_std IS
SELECT name
FROM STUDENT;
BEGIN
IF isEmp THEN
OPEN get_emp ;
FETCH get_emp INTO name_ ;
CLOSE get_emp ;
ELSE
OPEN get_std ;
FETCH get_std INTO name_ ;
CLOSE get_std ;
END IF;
RETURN name_;
END Get_Details_On_Condition;

Answer 2

Using if .. else construct is not proper (neither supported). You can use REF cursor to achieve the same like below.
DECLARE type cur1 REF CURSOR;
c1 cur1;
BEGIN
IF (variable1 := 'true') THEN
OPEN c1 FOR 'SELECT * FROM STUDENT';
ELSE
OPEN c1 FOR 'SELECT * FORM EMP';
END IF ;
END;
Idea taken from Oracle Community Forum Post
NOTE: I didn't included the entire code block (I mean cursor processing, closing etc) cause the main concern here is "How he will declare/define conditional cursor". So, pointed that particular in my code snippet. Since, rest of the part like processing the cursor and closing can be directly be found in Oracle specification.
For a complete code block, you can refer the answer given by Harsh

Answer 3

I would prefer to solve this without using dynamic SQL. If the code to process the results is the same for both tables, then it is reasonable to assume that the columns are the same (or equivalent) as well. My inclination would be to solve this using UNION and sub-queries:
DECLARE
CURSOR cur1 IS
SELECT a, b, c, d
FROM emp
WHERE NOT EXISTS
(SELECT *
FROM table1
WHERE s.key = 'xxxxx' AND t.VALUE = 'true')
UNION ALL
SELECT a, b, c, d
FROM student
WHERE EXISTS
(SELECT *
FROM table1
WHERE s.key = 'xxxxx' AND t.VALUE = 'true');
BEGIN
--Stored procedure logic
END;

Answer 4

The link provided by Rahul indicates the correct way to solve the problem. From the Oracle community forum post posted by Rahul, I have taken the code snippet through which the code could run successfully.
Rahul: Please do not take this as a redundant answer as I could not comment on your answer to help shyam to take the code snippet in the link posted by you.
Declare
TYPE cv_typ IS REF CURSOR;
cv cv_typ;
Begin
If(condition1 is TRUE) then
open cv FOR
'Select * from table_name1';
EXIT WHEN cv%NOTFOUND;
ELSE
open cv FOR
'Select * from table_name2';
EXIT WHEN cv%NOTFOUND;
End If;
CLOSE cv;
END;
Thanks & Regards,
Harsh

Answer 5

You can move the OPEN outside IF statement:
DECLARE type cur1 REF CURSOR;
c1 cur1;
vSQL VARCHAR2(1000);
BEGIN
IF (variable1 = 'true') THEN
vSQL := 'SELECT * FROM STUDENT';
ELSE
vSQL := 'SELECT * FORM EMP';
END IF;
OPEN c1 FOR vSQL;
--procedure logic
CLOSE c1;
END;