REF Cursor from Procedure PL/SQL - sql

Question

I am trying to troubleshoot a PL/SQL package. I found a similar example to explain my question as I am new to learning PL/SQL and how a cursor works with a procedure.
So for example:
CREATE OR REPLACE PROCEDURE emp_by_job (
p_job VARCHAR2,
p_emp_refcur IN OUT SYS_REFCURSOR
)
IS
BEGIN
OPEN p_emp_refcur FOR SELECT empno, ename FROM emp WHERE job = p_job;
END;
In this I see that p_job is defined as VARCHAR2. Then the SQL selects from EMP where job = p_job. All we've defined p_job as is VARCHAR2, not mapped to a field anywhere. How does the cursor know what to do with job = p_job, where does p_job's value come from?
Thank you!

Answer 1

A procedure doesn't do anything when it is compiled, it needs to be called/invoked. The value for p_job will be passed when the procedure is called. In the example below, emp_by_job is invoked from an anonymous pl/sql block with a value for the argument p_job of 'MANAGER'.
koen>CREATE OR REPLACE PROCEDURE emp_by_job (
2 p_job VARCHAR2,
3 p_emp_refcur IN OUT SYS_REFCURSOR
4 )
5 IS
6 BEGIN
7 OPEN p_emp_refcur FOR SELECT empno, ename FROM emp WHERE job = p_job;
8 END;
9* /
Procedure EMP_BY_JOB compiled
koen>set serveroutput on size 999999
koen>DECLARE
2 TYPE emp_t IS REF CURSOR;
3 l_emp emp_t;
4 l_emprow emp%ROWTYPE;
5 BEGIN
6 emp_by_job(p_job => 'MANAGER',p_emp_refcur => l_emp);
7 LOOP
8 FETCH
9 l_emp
10 INTO
11 l_emprow.empno,
12 l_emprow.ename;
13 EXIT
14 WHEN l_emp%notfound;
15 dbms_output.put_line(l_emprow.empno || ' ' || l_emprow.ename);
16 END LOOP;
17 END;
18* /
7698 BLAKE
7782 CLARK
7566 JONES
PL/SQL procedure successfully completed.
koen>