create table users (
  internal_id     number not null primary key,
  user_facing_id  number not null
)
/

create table demos (
  demo_code  varchar2(3) not null primary key,
  demo_desc   varchar2(60)
)
/

create table user_demo (
  internal_id  number references users(internal_id),
  demo_code  varchar2(3) references demos(demo_code),
  user_demo_comment   varchar2(100), 
  date_inserted  date
)
/

CREATE OR REPLACE PROCEDURE p_demo( 
  p_id             varchar2,  
  p_demo_code       varchar2, 
  clicked_on     varchar2 default to_char(sysdate,'MM/DD/YYYY hh24:mi:ss') 
) as 

l_internal_id            number;
l_user_demo_comment  varchar2(100);

cursor cur_demo is
select 'x' 
from user_demo 
where internal_id = l_internal_id
and demo_code = demo_code;  

r_demo   cur_demo%rowtype;

e_user_already_demoed  exception;

BEGIN 

  select internal_id  
  into l_internal_id   
  from users  
  where user_facing_id = p_id; 
   
  open cur_demo;   
  fetch cur_demo into r_demo;     
  if cur_demo%found then
      close cur_demo;
      raise e_user_already_demoed;    
  else       
      select demo_desc||' '||clicked_on      
      into l_user_demo_comment    
      from demos    
      where demo_code = p_demo_code; 
    
       insert into user_demo (      
          internal_id, demo_code, user_demo_comment, date_inserted    
       )  values (
         l_internal_id, p_demo_code, l_user_demo_comment, sysdate    
       );        

       commit; 
   end if; 
   
   close cur_demo; 
 
EXCEPTION 
  when e_user_already_demoed then     
    /* insert into log table (not null in real life) */ null; 
  when no_data_found then     
   /* inserts into log table (not null in real life) */ null; 
 commit; 
  
END p_demo;