Answer Posted / harinadh bolisetti

PL/SQL allows developers to define their own exceptions.
User can define the error/exception programmatically based on the business rule.

1. Define Exception
---------------------
We need to define the exception before we raise and handle. User Exceptions are defined using keyword EXCEPTION in declaration section of the block.
The syntax is as follows

<exception_name> EXCEPTION ;


2. Raise the Exception
--------------------------
Once the exceptions are defined , they need to be raised anywhere in the body depending upon predefined logic. User exceptions are raised using the keyword RAISE.
Syntax is as shown below

RAISE <exception_name>

3. Handle the Exception.
--------------------------
User exception are handled in the same way predefined exceptions are handled. They are handled in exception block using WHEN .. THEN keyword
Syntax is as shown below

WHEN <exception_name> THEN


example
----------------
DECLARE
low_sal EXCEPTION;
min_sal NUMBER:= 10000;
new_sal NUMBER:= 8000;
BEGIN
INSERT INTO EMP_EXC_DEMO(EMPNO, DEPTNO, SAL)
VALUES (4000,20,new_sal);
IF new_sal < min_sal THEN
RAISE low_sal;
END IF;
commit;
EXCEPTION
WHEN low_sal THEN
Rollback;
DBMS_OUTPUT.PUT_LINE ('Salary is less than '||min_sal);
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE (SQLERRM);
END;

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