解決用B表跟新A表數據，若是A表中沒有，則把B表的數據插入A表（merge into）

做用：merge into 解決用B表跟新A表數據，若是A表中沒有，則把B表的數據插入A表；

語法：

MERGE INTO [your table-name] [rename your table here]

USING ( [write your query here] )[rename your query-sql and using just like a table]

ON ([conditional expression here] AND [...]...)

WHEN MATHED THEN [here you can execute some update sql or something else ]

WHEN NOT MATHED THEN [execute something else here ! ]

-------------------------------------實例-----------------------------------------------------------------

merge into tfa_alarm_act_nms a
using (select FP0,FP1,FP2,FP3,REDEFINE_SEVERITY
from tfa_alarm_status) b
on (a.fp0=b.fp0 and a.fp1=b.fp1 and a.fp2=b.fp2 and a.fp3=b.fp3)
when matched then update set a.redefine_severity=b.redefine_severity
when not matched then insert (a.fp0,a.fp1,a.fp2,a.fp3,a.org_severity,a.redefine_severity,a.event_time
,a.int_id)
values (b.fp0,b.fp1,b.fp2,b.fp3,b.REDEFINE_SEVERITY,b.redefine_severity,sysdate,7777778);

做用：利用表 tfa_alarm_status跟新表tfa_alarm_act_nms 的b.redefine_severity，條件是a.fp0=b.fp0 and a.fp1=b.fp1 and a.fp2=b.fp2 and a.fp3=b.fp3，若是tfa_alarm_act_nms表中沒有該條件的數據就插入。

若是你的數據量很大，此sql效率很是高。

 

 

 

 MERGE INTO ds_plan a
　　USING sm_plan b
　　ON(a.plan_id=b.plan_id)
　　WHEN NOT MATCHED THEN insert (plan_id) values (b.plan_id)