The following code is compiled successfully in Oracle PL/SQL:
BEGIN
NULL;
-- some codes
END LOOP;
My question is, using END LOOP without any loop is an error or can has any special meaning?
loop, in this context, doesn't represent end of a loop - it is a label. You could have used e.g.
SQL> begin
2 null;
3 end tahzibi;
4 /
PL/SQL procedure successfully completed.
SQL>
and - as you can see - it works as well.
How come? That's - I believe - related to named PL/SQL blocks (we know as "functions" or "procedures") (your code represents an anonymous PL/SQL block).
A simple example:
SQL> create or replace procedure p_test is --> procedure name is P_TEST
2 begin
3 null;
4 end p_test; --> best practice says that we should END it with its name; hence P_TEST after END keyword
5 /
Procedure created.
SQL>
In anonymous PL/SQL block, that label isn't related to any name (obviously). Oracle allows it, but - at the same time - ignores it. You can use it, but don't have to - and we usually don't.
If you wanted to make some sense in it, then create a label in your code and end begin-end part of it with that label so that it improves readability, especially in complex PL/SQL procedures. Something like this:
SQL> begin
2 <<compute_salary>> --> this is the label
3 begin
4 null;
5 -- here goes code that computes salaries and
6 -- spreads thorugh 30 lines of code
7 end compute_salary; --> end that BEGIN-END block with the label name
8 end;
9 /
PL/SQL procedure successfully completed.
SQL>