个人理解MERGE INTO函数是个逻辑扩展函数，类似if-else函数

eg:

MERGE INTO A_TEST A USING (select B.id,B.NAME,B.YEAR from B_TEST B) C ON (A.id=C.id)

WHEN MATCHED THEN

WHEN NOT MATCHED THEN

INSERT(A.ID,A.NAME,A.YEAR) VALUES(C.ID,C.NAME,C.YEAR);