Convert substring function from SQL Server to Oracle

Question

I am converting a large application written for SQL Server to Oracle and have encountered a difference in how the substring function is called between the two database systems.
In SQL Server:
select substring('xyz'1,2)
In Oracle:
select substr('xyz',1,2)
Is there a way to establish a user-defined operator to map the substring call to a substr call so I don't have to change the application code?
Is the user-defined function a way to do this?
Which is better?

Answer 1

If you want to be able to use the code that has substring in it, without modifying it, and have it do the same thing as substr, then try running the script below. It will create a user-defined function named substring that will cause substring to act like substr.
CREATE OR REPLACE FUNCTION substring
(p_string IN VARCHAR2,
p_start IN VARCHAR2,
p_end IN VARCHAR2 DEFAULT NULL)
RETURN VARCHAR2
IS
v_string VARCHAR2 (100);
BEGIN
IF p_end IS NULL
THEN
SELECT SUBSTR (p_string, p_start)
INTO v_string
FROM DUAL;
ELSE
SELECT SUBSTR (p_string, p_start, p_end)
INTO v_string
FROM DUAL;
END IF;
RETURN v_string;
END substring;
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