作用：使用一条sql语句进行insert或者update操作，如果存在就update，如果不存在就insert
语法：
MERGE INTO table_name t1 USING (table|view|sub_query) t2 ON (join condition) WHEN MATCHED THEN UPDATE table_name SET col1 =.., col2 =..WHEN NOT MATCHED THEN INSERT (..) VALUES (..);
注意：由于Merge在oracle中最先是用于整表更新，所以t2中的数据每一条都会和t1进行on中的条件比对
insert或者update的记录数和t2中的记录数相同，当然也可在update后加where条件控制
eg：
MERGE INTO CUSTOMIZATION C1 USING (SELECT ‘isMonitor‘ AS OPERATION_KEY, ‘0001‘ AS USER_ID , ‘0‘ AS OPERATION_VALUE FROM DUAL) C2 ON (C1.OPERATION_KEY = C2.OPERATION_KEY AND C1.USER_ID = C2.USER_ID) WHEN MATCHED THEN UPDATE SET C1.OPERATION_VALUE = C2.OPERATION_VALUE WHERE C1.OPERATION_KEY = C2.OPERATION_KEY AND C1.USER_ID = C2.USER_ID WHEN NOT MATCHED THEN INSERT (OPERATION_KEY,OPERATION_VALUE,USER_ID) VALUES(C2.OPERATION_KEY,C2.OPERATION_VALUE,C2.USER_ID);
首次插入时表中没有符合条件数据，则插入数据，
只更改operation_value, operation_key 和user_id存在时更新数据,operation_value更新为1
MERGE INTO CUSTOMIZATION C1 USING (SELECT ‘isMonitor‘ AS OPERATION_KEY, ‘0001‘ AS USER_ID , ‘1‘ AS OPERATION_VALUE FROM DUAL) C2 ON (C1.OPERATION_KEY = C2.OPERATION_KEY AND C1.USER_ID = C2.USER_ID) WHEN MATCHED THEN UPDATE SET C1.OPERATION_VALUE = C2.OPERATION_VALUE WHERE C1.OPERATION_KEY = C2.OPERATION_KEY AND C1.USER_ID = C2.USER_ID WHEN NOT MATCHED THEN INSERT (OPERATION_KEY,OPERATION_VALUE,USER_ID) VALUES(C2.OPERATION_KEY,C2.OPERATION_VALUE,C2.USER_ID);
Merge into(oracle),布布扣,bubuko.com
原文：http://www.cnblogs.com/wishyouhappy/p/3791785.html