Calculate the max and sum value by weird way !!!

Question

this code calculate the sum value without sum clause :-
DECLARE
x NUMBER;
y NUMBER := 0;
CURSOR cur_sal
IS
SELECT sal
FROM emp;
BEGIN
OPEN cur_sal;
LOOP
FETCH cur_sal
INTO x;
EXIT WHEN cur_sal%NOTFOUND;
y := y + x;
END LOOP;
CLOSE cur_sal;
DBMS_OUTPUT.put_line ('sum sal without using sum function = ' || y);
END;
and this code calculate the max value without max clause :-
DECLARE
x NUMBER;
y NUMBER := 0;
CURSOR cur_sal
IS
SELECT sal
FROM emp;
BEGIN
OPEN cur_sal;
LOOP
FETCH cur_sal
INTO x;
EXIT WHEN cur_sal%NOTFOUND;
IF (x > y)
THEN
y := x;
END IF;
END LOOP;
CLOSE cur_sal;
DBMS_OUTPUT.put_line ('max sal without using max function = ' || y);
END;
the Question is : how suppose that's happen ?
what's the secret in those codes ?
it's just new idea for me , but I don't understand !
is there any name for this way in ( Oracle® Database PL/SQL User's Guide and Reference ) ?
if not , so please anyone give me any help to understand those codes !

Answer 1

Secret? What secret? It slowly and inefficiently fetch each row one at a time and consecutively add them together you get a sum. What the first, horribly inefficient, cursor loop is doing is roughly the equivalent of determining how many rivets are in a bucket by dumping them on the floor and picking them up one at a time rather than weighing one, weighing all, and then doing a simple division. The second loop does the same, horribly inefficient thing, by picking up each rivet and seeing if it is bigger than the previous one.
Cursor loops are obsolete and this code is about as inefficient as you can get without using an Excel macro.