Function: Error Handling
Description:

Types of Errors:

DUP_VAL_ON_INDEX	Unique constraint voilation
TIMEOUT_ON_RESOURCE	Time out occurred
TRANSACTION_BACKED_OUT	The transaction was rolled back
INVALID_CURSOR	Illegal cursor operation
NO_DATA_FOUND	No data found
TOO_MANY_ROWS	A Select .. INTO statement had more than one match
CURSOR_ALREADY_OPEN	Attempted to open a cursor that was already open.
ROWTYPE_MISMATCH	PL/SQL cursor variable was assigned an incompatible row type.
OTHERS	Other error messages not predefined

Control passing to an exception handler

DECLARE A EXCEPTION BEGIN .... RAISE A ... EXCEPTION WHEN A THEN ....

SQLCODE and SQLERRM

SQLCODE - Oracle Error Number
SQLERRM - Descriptive Error Message

PRAGMA EXCEPTION_INIT

(exception_name, Oracle error number)
DECLARE 
	e_MissingNull EXCEPTION;
	PRAGMA EXECEPTION_INIT(e_MissingNULL,-1400);
BEGIN
	INSERT INTO temp (id) values (NULL);
EXCEPTION
	WHEN e_MissingNull then
		...
END;