gistfile1.txt

  create sequence current_user_id;                                                                  
                                                                                                    
  create function set_current_user_id(user_id integer) returns integer language sql as $f$          
    select setval('current_user_id', $1::integer)::integer;                                         
  $f$;                                                                                              
                                                                                                    
  create function current_user_id() returns integer language sql as $f$                             
    select currval('current_user_id')::integer;                                                     
  $f$;                                                                                              
                                                                                                    
  create table products(id integer primary key, price numeric);                                     
  insert into products values (1, 1.99), (2, 2.50);                                                 
                                                                                                    
  create function price(product_id integer, user_id integer) returns numeric language sql as $f$    
    select price + $2 from products where products.id = $1;                                         
  $f$;                                                                                              
                                                                                                    
  create view product_prices as (                                                                   
    select products.id, price, (select price(products.id, current_user_id())) as custom_price       
    from products);                                                                                 
                                                                                                    
  select set_current_user_id(1);                                                                    
  select * from product_prices;                                                                     
                                                                                                    
  select set_current_user_id(4);                                                                    
  select * from product_prices;