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样式1：

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

样式2：

1. update xcs_user_credit_score a1
2. inner join xcs_user_credit_score a2
3. on a1.uid=a2.uid
4. set a1.user_currday_score=a1.user_currday_increment_score+a2.user_currday_score
5. where a1.pt_day='2017-09-20' and a2.pt_day='2017-09-19'
6. ;

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：

1. --sub:
2. update xcs_user_credit_score a1,xcs_user_credit_score a2
3. set a1.user_currday_score=(case when a2.user_currday_score-10>0 then a2.user_currday_score-10 else 0 end)
4. where a1.pt_day='2017-09-20' and a2.pt_day='2017-09-19'
5. and a1.uid=a2.uid
6. 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)
7. and a2.user_currday_score>0
8. ;
10. --plus:
11. update xcs_user_credit_score a1,xcs_user_credit_score a2
12. set a1.user_currday_score=(case when a1.user_currday_score+10<0 then a1.user_currday_score+10 else 0 end)
13. where a1.pt_day='2017-09-20' and a2.pt_day='2017-09-19'
14. and a1.uid=a2.uid
15. 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)
16. and a1.user_currday_score<0
17. ;