Defined variable and substitution variables

Question

Are both of these internally treated in the same way by the Oracle database?
for example a defined variable
DEFINE p_grade = a
and if I use a substitution variable p_grade
DECLARE
p_grade VARCHAR2(10);
v_name VARCHAR2(10);
BEGIN
SELECT last_name
INTO v_name
FROM employees;
WHERE job_id = &p_grade
END;
Edited by: user6287828 on Feb 24, 2009 10:52 AM

Answer 1

Hi,
What you're calling a "defined variable" is nothing but a substitution variable.
DEFINE  p_grade = ais just one way of setting the value of the substitution variable p_grade.
When you later use that variable, for example
WHERE job_id = &p_gradethere is no way of telling how p_grade got its value (if it has one).
Avoid using the same name for two different types of variables.
For example:
DECLARE
    p_grade VARCHAR2(10);   -- Local variable declared
    v_name VARCHAR2(10);
BEGIN
    SELECT  last_name
    INTO    v_name
    FROM    employees
    WHERE   job_id = &p_grade;    -- Substitution variable used
END;In the second line, you are creating a local VARCHAR2 variable called p_grade that is never used. It has nothing to do with the substitution variable p_grade (unless the value of that substitution variable happens to be p_grade,
DEFINE  p_grade = p_grade)
If you do use the same name for differnt types of variables, SQL*Plus may keep them straight, but no one else (including you) will.