1、 方法1：
UPDATE PUR_PO p1
set (a, b) =
(select p1.a - p2.total_amount, p1.b + p2.total_amount
from PUR_ACCEPT p2
where p1.form_no = p2.po_no
and p2.FORM_NO = 1021
AND p2.ACCEPT_TYPE_VALUE = 1)
where exists (select *
from PUR_ACCEPT p2
where p1.form_no = p2.po_no
and p2.FORM_NO = 1021
AND p2.ACCEPT_TYPE_VALUE = 1);
2、 方法2：
Merge into PUR_PO A
Using (SELECT TOTAL_AMOUNT, PO_NO
FROM PUR_ACCEPT
WHERE FORM_NO = 1021
AND ACCEPT_TYPE_VALUE = 1) B
on (A.FORM_NO = B.PO_NO)
when Matched then
Update set A.a = A.a - B.TOTAL_AMOUNT, A.b = A.b + b.TOTAL_AMOUNT;