oracle当满足条件时将第一条数据的pk更新到第二条的pk2中去，报错

Question

update a hf
set hf.pk_id2 = hl.pk_id
where hl.project_id = '002'
and hl.show_no in
(select hf.show_no
from a hf
where hf.project_id = '00c')
and hl.estimate_name in
(select hf.estimate_name
from a hf
where hf.project_id = '00c')
数据在一张表了，存的两颗树，当树的节点，名称相同时，把第一棵树的pk存到第二颗树的pk2中去。
hl和hf都是给a表起的别名。大概就是循环更新的意思，找了半天资料还是写不出来，希望大神们帮帮忙，谢谢了

Answer 1

update a2 set a2.pk2 = a1.pk where a1.节点 = a2.节点 and a1.名称 = a2.名称

(select * from a where project_id = 1) a1

(select * from a where project_id = 2) a2

是这个意思吗？