Oracle 的 bulk collect用法

採用bulk collect可以將查詢結果一次性地載入到collections中，而不是透過cursor一條一條地處理。

可以在select into,fetch into,returning into語句使用bulk collect。

注意：在使用bulk collect時，所有的into變數都必須是collections。

create table t_test as
  select object_id, object_name, object_type
    from dba_objects
   where wner = 'TEST';

1、在select into語句中使用bulk collect

declare
  type object_list is table of t_test.object_name%type;
  objs object_list;
begin
  select object_name bulk collect
    into objs
    from t_test
   where rownum <= 100;
  for r in objs.first .. objs.last loop
    dbms_output.put_line(' objs(r)=' || objs(r));
  end loop;
end;
/

2、在fetch into中使用bulk collect

declare
  type objecttab is table of t_test%rowtype;
  objs objecttab;
  cursor cob is
    select object_id, object_name, object_type
      from t_test
     where rownum <= 10;
begin
  open cob;
  fetch cob bulk collect
    into objs;
  close cob;
  for r in objs.first .. objs.last loop
    dbms_output.put_line(' objs(r)=' || objs(r).object_name);
  end loop;
end;
/

以上為把結果集一次fetch到collect中，我們還可以透過limit引數，來分批fetch資料，如下：

declare
  type objecttab is table of t_test%rowtype;
  objs objecttab;
  cursor cob is
    select object_id, object_name, object_type
      from t_test
     where rownum <= 10000;
begin
  open cob;
  loop
    fetch cob bulk collect
      into objs limit 1000;
    exit when cob%notfound;
    dbms_output.put_line('count:' || objs.count || ' first:' || objs.first ||
                         ' last:' || objs.last);
    for r in objs.first .. objs.last loop
      dbms_output.put_line(' objs(r)=' || objs(r).object_name);
    end loop;
  end loop;
  close cob;
end;
/

你可以根據實際來調整limit引數的大小，來達到最優的效能。limit引數會影響到PGA的使用率。

3、在returning into中使用bulk collect

declare
  type id_list is table of t_test.object_id%type;
  ids id_list;
  type name_list is table of t_test.object_name%type;
  names name_list;
begin
  delete from t_test
   where object_id <= 87510 returning object_id, object_name bulk collect into ids,
   names;
  dbms_output.put_line('deleted ' || sql%rowcount || ' rows:');
  for i in ids.first .. ids.last loop
    dbms_output.put_line('object #' || ids(i) || ': ' || names(i));
  end loop;
end;
/