批量处理数据 bulk collect

在日常开发中，对于用到游标的情况，使用批量操作比逐条处理效果更好， 如下例子：

DECLARE
  TYPE prod_tab IS TABLE OF products%ROWTYPE;
  products_tab prod_tab := prod_tab();
  start_time   NUMBER;
  end_time     NUMBER;
  CURSOR products_data IS
    SELECT * FROM products;
BEGIN
  start_time := dbms_utility.get_time;
  
  OPEN products_data;
  LOOP
    products_tab.extend;
    FETCH products_data
      INTO products_tab(products_tab.last);
    IF products_data%NOTFOUND
    THEN
      products_tab.delete(products_tab.last);
      EXIT;
    END IF;
  END LOOP;
  CLOSE products_data;
  
  end_time := dbms_utility.get_time;
  
  dbms_output.put_line('conventional(' || products_tab.count || ')
                       :' || to_char(end_time - start_time));

  start_time := dbms_utility.get_time;
  
  OPEN products_data;
  FETCH products_data BULK COLLECT
    INTO products_tab;
  CLOSE products_data;
  
  end_time := dbms_utility.get_time;
  
  dbms_output.put_line('bulk COLLECT(' || products_tab.count || ')
                       :' || to_char(end_time - start_time));
END;