简单的送分的问题

Question

update insuredaccount set en_lastyear_remain=(select en_fare from insuredaccountall
where insuredaccountall.l_insured_id=insuredaccount.l_insured_id and insuredaccountall.C_ACCOUNT='A')
where INSUREDACCOUNT.C_ACCOUNT='A' and exists
（select 1 from insuredaccountall
where insuredaccountall.l_insured_id=insuredaccount.l_insured_id and insuredaccountall.C_ACCOUNT='A')

Answer 1

仍然报错：
ORA-01407: 无法更新 ("GXDBO"."INSUREDACCOUNT"."EN_LASTYEAR_REMAIN") 为 NULL

Answer 2

问题已经解决
原因是select en_fare from insuredaccountall
where insuredaccountall.l_insured_id=insuredaccount.l_insured_id and insuredaccountall.C_ACCOUNT='A'的返回值确实有full