mysql关联更新

样式一： 

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;

样式二：

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'
;