set serveroutput on in oracle procedure

Question

I've created a simple procedure. In this procedure i want to output some data. However where ever i put set serveroutput on

it says

Error(26,5): PLS-00103: Encountered the symbol "SERVEROUTPUT" when expecting one of the following: . ( ) , * @ % & = - + < / > at in is mod remainder not rem => <> or != or ~= >= <= <> and or like like2 like4 likec as between || multiset member submultiset

It doesn't matter where i put it, it keeps saying it.

create or replace PROCEDURE discount  

is --- signature 

BEGIN --- executable part

update dvd set me_our_price = me_our_price*0.90 WHERE me_release_year = 2011;
update dvd set me_our_price = me_our_price*0.80 WHERE me_release_year = 2010;

update bluray set me_our_price = me_our_price*0.95 WHERE me_release_year = 2011;
update bluray set me_our_price = me_our_price*0.90 WHERE me_release_year = 2010;


DBMS_OUTPUT.PUT_LINE(' Blurays '); 
for i in ( 
SELECT e.mo_title, e.mo_bluray.me_list_price as me_list_price, e.mo_bluray.me_our_price    as  me_our_price FROM movie e  where e.mo_bluray is not null
 ) 
loop 

DBMS_OUTPUT.PUT_LINE(i.mo_title|| '  ' || i.me_list_price|| '  ' || i.me_list_price); 

end loop; 

DBMS_OUTPUT.PUT_LINE(' DVDs '); 
for i in ( 
set serveroutput on
SELECT e.mo_title, e.mo_dvd.me_list_price as me_list_price, e.mo_dvd.me_our_price as      me_our_price FROM movie e  where e.mo_dvd is not null
 ) 
loop 
DBMS_OUTPUT.PUT_LINE(i.mo_title|| '  ' || i.me_list_price|| '  ' || i.me_list_price); 
end loop; 


END discount; 

Answer 1

To understand the use of "SET SERVEROUTPUT ON" I will take an example

DECLARE
a number(10)  :=10;
BEGIN
dbms_output.put_line(a) ;
dbms_output.put_line('Hello World ! ')  ;
END ;

With an output : PL/SQl procedure successfully completed i.e without the expected output

And the main reason behind is that ,whatever we pass inside dbms_output.put_line(' ARGUMENT '/VALUES) i.e. ARGUMENT/VALUES , is internally stored inside a buffer in SGA(Shared Global Area ) memory area upto 2000 bytes .

*NOTE :***However one should note that this buffer is only created when we use **dbms_output package. And we need to set the environment variable only once for a session !!

And in order to fetch it from that buffer we need to set the environment variable for the session . It makes a lot of confusion to the beginners that we are setting the server output on ( because of its nomenclature ) , but unfortunately its nothing like that . Using SET SERVER OUTPUT ON are just telling the PL/SQL engine that

*Hey please print the ARGUMENT/VALUES that I will be passing inside dbms_output.put_line
and in turn PL/SQl run time engine prints the argument on the main console .

I think I am clear to you all . Wish you all the best . To know more about it with the architectural structure of Oracle Server Engine you can see my answer on Quora http://qr.ae/RojAn8

And to answer your question "One should use SET SERVER OUTPUT in the beginning of the session. "