What is purpose of NULL at the end of this loop? - oracle

Question

Revising an old program. It issues NULL; and the end of this loop.
Why? What is it supposed to do? Nothing as far as I can tell.
Here is the loop:
--Price Break Loop
OPEN c_price_breaks;
<<c_price_breaks_loop>>
l_prc_brk_count := 1;
LOOP
dbms_output.put_line('Price break loop..');
fnd_file.put_line(fnd_file.log,'Price break loop..');
--FOR prc_brk_cnt IN 1..L_prc_brk_count LOOP
FETCH c_price_breaks INTO l_price_override, l_ship_to_organization_id_pb, l_ship_to_organization_code_pb, l_ship_to_location_id_pb, l_ship_to_location_code_pb, l_quantity;
EXIT WHEN c_price_breaks%NOTFOUND;
--Inserting into line location interface table
INSERT INTO PO.PO_LINE_LOCATIONS_INTERFACE (
INTERFACE_LINE_LOCATION_ID,
INTERFACE_HEADER_ID,
INTERFACE_LINE_ID,
SHIPMENT_TYPE,
SHIPMENT_NUM,
SHIP_TO_ORGANIZATION_ID,
SHIP_TO_LOCATION_ID,
QUANTITY,
UNIT_OF_MEASURE,
PRICE_OVERRIDE,
CREATION_DATE
) VALUES (
po_line_locations_interface_s.nextval, --INTERFACE_LINE_LOCATION_ID,
po_headers_interface_s.currval, --INTERFACE_HEADER_ID,
po_lines_interface_s.currval, --INTERFACE_LINE_ID,
'QUOTATION', --SHIPMENT_TYPE,
l_prc_brk_count, --SHIPMENT_NUM,
l_ship_to_organization_id_pb, --SHIP_TO_ORGANIZATION_ID,
l_ship_to_location_id_pb, --SHIP_TO_LOCATION_ID,
l_quantity, --QUANTITY,
l_unit_of_measure, --UOM
l_price_override, --PRICE_OVERRIDE
SYSDATE --CREATION_DATE,
);
l_prc_brk_count := l_prc_brk_count+1;
<<END_of_c_price_breaks_loop>>
NULL;
END LOOP; --END of Price break loop

Answer 1

Yes, the NULL is required while you have a label at the end of the PL/SQL block formed by the LOOP.
The Oracle documentation for the GOTO statement states:
GOTO Statement
The GOTO statement branches unconditionally to a statement label or block label. The label must be unique within its scope and must precede an executable statement or a PL/SQL block. The GOTO statement transfers control to the labelled statement or block.
The <<END_of_c_price_breaks_loop>> is a label and it must precede an executable statement or a PL/SQL block; NULL; is such a statement.
DECLARE
l_prc_brk_count PLS_INTEGER;
BEGIN
<<c_price_breaks_loop>>
l_prc_brk_count := 1;
LOOP
dbms_output.put_line('Price break loop..');
EXIT WHEN l_prc_brk_count > 3;
l_prc_brk_count := l_prc_brk_count+1;
<<END_of_c_price_breaks_loop>>
NULL;
END LOOP; --END of Price break loop
END;
/
Outputs:
Price break loop..
Price break loop..
Price break loop..
Price break loop..
Removing the NULL;
DECLARE
l_prc_brk_count PLS_INTEGER;
BEGIN
<<c_price_breaks_loop>>
l_prc_brk_count := 1;
LOOP
dbms_output.put_line('Price break loop..');
EXIT WHEN l_prc_brk_count > 3;
l_prc_brk_count := l_prc_brk_count+1;
<<END_of_c_price_breaks_loop>>
END LOOP; --END of Price break loop
END;
/
Gives:
ORA-06550: line 13, column 3:
PLS-00103: Encountered the symbol "END" when expecting one of the following:
( begin case declare exit for goto if loop mod null raise
return select update while with <an identifier>
<a double-quoted delimited-identifier> <a bind variable> <<
continue close current delete fetch lock insert open rollback
savepoint set sql execute commit forall merge pipe purge
Removing the label:
DECLARE
l_prc_brk_count PLS_INTEGER;
BEGIN
<<c_price_breaks_loop>>
l_prc_brk_count := 1;
LOOP
dbms_output.put_line('Price break loop..');
EXIT WHEN l_prc_brk_count > 3;
l_prc_brk_count := l_prc_brk_count+1;
END LOOP; --END of Price break loop
END;
/
Gives:
Price break loop..
Price break loop..
Price break loop..
Price break loop..
db<>fiddle here

Answer 2

The null is there because there has to be a statement after a label. If you try to run this block, for example
declare
l_cnt integer := 0;
begin
loop
exit when l_cnt > 1;
l_cnt := l_cnt + 1;
<<foo>>
end loop;
end;
you'll get a syntax error because the label foo doesn't have an executable statement after it. If you add a null;, the block compiles
declare
l_cnt integer := 0;
begin
loop
exit when l_cnt > 1;
l_cnt := l_cnt + 1;
<<foo>>
null;
end loop;
end;
Now, it doesn't appear that either of the labels in the code you posted are actually doing anything useful themselves (other than maybe functioning as comments?). Unless you have code somewhere else that has a goto one of these labels, you could eliminate both the c_price_breaks_loop label and the END_of_c_price_breaks_loop label and then you can get rid of the null; statement.