oracle bucket collect(批量查询)

采用bulk collect可以将查询结果一次性地加载到collections中，而不是通过cursor一条一条地处理。

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

注意：在使用bulk collect时，所有的into变量都必须是collections。

 

create table t_test as

  select object_id, object_name, object_type

    from dba_objects

   where wner = 'TEST';

 

1、在select into语句中使用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;

/

以上为把结果集一次fetch到collect中，我们还可以通过limit参数，来分批fetch数据，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;

/

你可以根据实际来调整limit参数的大小，来达到最优的性能。limit参数会影响到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;

  id
9408
s 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;