mysql关联更新update

样式1：

update xcs_user_credit_score a1,xcs_user_credit_score a2   set a1.user_currday_score=a1.user_currday_increment_score+a2.user_currday_score where a1.pt_day='2017-09-20' and a2.pt_day='2017-09-19'   and a1.uid=a2.uid;

样式2：

update xcs_user_credit_score a1 inner join xcs_user_credit_score a2    on a1.uid=a2.uid   set a1.user_currday_score=a1.user_currday_increment_score+a2.user_currday_score where a1.pt_day='2017-09-20' and a2.pt_day='2017-09-19';

突然发现mysql的一些sql语法也很神奇，像这样式的sql语句，在oracle中是行不通的，需要其他的形式。
另外的几个例子：

--sub:update xcs_user_credit_score a1,xcs_user_credit_score a2   set a1.user_currday_score=(case when a2.user_currday_score-10>0 then a2.user_currday_score-10 else 0 end) where a1.pt_day='2017-09-20' and a2.pt_day='2017-09-19'   and a1.uid=a2.uid   and (a1.seqing_score=0 and a1.user_silent_score=0 and a1.jubao_score=0 and a1.chengpaopao_score=0 and a1.weifan_score=0 and a1.upper_manage_score=0 and a1.pay_active_score=0 and a1.view_active_score=0 and a1.message_active_score=0 and a1.gift_active_score=0 and a1.live_active_score=0)   and a2.user_currday_score>0;--plus:update xcs_user_credit_score a1,xcs_user_credit_score a2   set a1.user_currday_score=(case when a1.user_currday_score+10<0 then a1.user_currday_score+10 else 0 end) where a1.pt_day='2017-09-20' and a2.pt_day='2017-09-19'   and a1.uid=a2.uid   and (a1.seqing_score=0 and a1.user_silent_score=0 and a1.jubao_score=0 and a1.chengpaopao_score=0 and a1.weifan_score=0)   and a1.user_currday_score<0;