bulk collect forall等批量更新优化方法比对【视频】

内容：批量更新优化方法比对
--使用场景：日常运维时常会出现根据一个表的内容去更新另一个表内容；
--涉及方法：1.普通游标   2.批量绑定游标 3.merge

构造数据:
create table t1 as select * from dba_objects where object_id is not null;
create table t2 as select * from dba_objects where object_id is not null;

1.普通游标

begin
for c1 in (select object_id,object_name from t2) loop
update t1 set t1.object_name=c1.object_name
where t1.object_id=c1.object_id;
end loop;
end;
/

2.批量绑定游标

declare
c_nt number;
cursor c1 is select object_id,object_name from t2;
type t_t1 is table of  c1%rowtype;
v_t1 t_t1;
begin
c_nt :=0;
open c1;
loop
fetch  c1 bulk collect into v_t1 limit 5000;
forall idx in 1..v_t1.count 
update t1 set t1.object_name=v_t1(idx).object_name
where t1.object_id=v_t1(idx).object_id;
   if c_nt=5000 then
   commit;
   end if;
   c_nt :=c_nt+1;
exit when c1%NOTFOUND;
end loop;
rollback;
close c1;
end;
/

3.merge使用

merge into t1
using t2
on (t1.object_id=t2.object_id)
when matched then
update set  t1.object_name=t2.object_name;

merge into t1
using t3
on (t1.object_id=t3.object_id)
when matched then
update set  t1.object_name=t3.object_name;

4.注意几个问题
(1) merge索引使用
(2) 批量绑定更新limit数量大小影响

5.小结：
merge:快捷，但不够灵活，速度较快
批量绑定游标:较灵活，速度较快
普通游标：较慢，较灵活

merge into t1
using t3
on (t1.object_id=t3.object_id)
when matched then
update set  t1.object_name=t3.object_name;

update t2 set object_name='ZBK' where rownum<11;
select count(1) from t1 where object_name='ZBK';