Merge into 多表关联查询插入 对比 Replace into

假设有以下2张源表A和表B
     A（pkey,a1,a2,a3）
     B（pkey.b1,b2,b3）
     与此同时数据库里也有了一张目标表C，C的表结构为
     C（pkey,a1,b1,c1,a2,b2)

把A和B中对应字段的数据同步到C中，同时c1的数据给个默认值：建表语句如下：

drop table A;
drop table B;
drop table C;

create table A(
       pkey varchar2(10),
	   a1 varchar2(10),
	   a2 varchar2(10),
	   a3 varchar2(10),
       PRIMARY KEY (pkey) 
);

create table B(
       pkey varchar2(10),
	   b1 varchar2(10),
	   b2 varchar2(10),
	   b3 varchar2(10),
       PRIMARY KEY (pkey) 
);

create table C(
       pkey varchar2(10),
	   a1 varchar2(10),
	   b1 varchar2(10),
	   c1 varchar2(10),
	   a2 varchar2(10),
	   b2 varchar2(10),
       PRIMARY KEY (pkey) 
);

INSERT INTO A (pkey,a1,a2,a3) VALUES(1,'a','a','a');
INSERT INTO A (pkey,a1,a2,a3) VALUES(2,'a1','a1','a1');
INSERT INTO A (pkey,a1,a2,a3) VALUES(3,'a3','a3','a3');
INSERT INTO A (pkey,a1,a2,a3) VALUES(4,'a4','a4','a4');
INSERT INTO B (pkey,b1,b2,b3) VALUES(1,'b','b','b');
INSERT INTO B (pkey,b1,b2,b3) VALUES(2,'b1','b1','b1');
INSERT INTO B (pkey,b1,b2,b3) VALUES(3,'b2','b2','b2');

Merge into 为：

MERGE INTO C tmpC
USING (
  SELECT
        tmpA.pkey,
        tmpA.a1,
        tmpB.b1,
        'c1的默认值',
        tmpA.a2,
        tmpB.b2 
      FROM
        ( SELECT pkey, a1, a2 FROM A )tmpA , 
        ( SELECT pkey, b1, b2 FROM B )tmpB  	
    WHERE tmpB.pkey = tmpA.pkey 
)tmp ON(tmpC.pkey=tmp.pkey)
WHEN MATCHED THEN
     UPDATE SET 
            tmpC.a1=tmp.a1,
            tmpC.b1=tmp.b1,
            tmpC.c1='c1的默认值',
            tmpC.a2=tmp.a2,
            tmpC.b2=tmp.b2
WHEN NOT MATCHED THEN 
     INSERT (pkey,a1, b1,c1,a2,b2)VALUES(tmp.pkey,tmp.a1,tmp.b1,'c1的默认值',tmp.a2,tmp.b2);

若以A的主键Pkey为主，使用左连接

MERGE INTO C tmpC
USING (
  SELECT
    tmpA.pkey,
    tmpA.a1,
    tmpB.b1,
    'c1的默认值',
    tmpA.a2,
    tmpB.b2 
  FROM
    ( SELECT pkey, a1, a2 FROM A )tmpA left join ( SELECT pkey, b1, b2 FROM B )tmpB  	on tmpB.pkey = tmpA.pkey 
)tmp ON(tmpC.pkey=tmp.pkey)
WHEN MATCHED THEN
     UPDATE SET 
            tmpC.a1=tmp.a1,
            tmpC.b1=tmp.b1,
            tmpC.c1='c1的默认值',
            tmpC.a2=tmp.a2,
            tmpC.b2=tmp.b2
WHEN NOT MATCHED THEN 
     INSERT (pkey,a1, b1,c1,a2,b2)VALUES(tmp.pkey,tmp.a1,tmp.b1,'c1的默认值',tmp.a2,tmp.b2);

在Mysql中的相同语句为：

INSERT REPLACE INTO C ( pkey, a1, b1, c1, a2, b2 )
VALUES
	(
	SELECT
		tmp_A.pkey,
		tmp_A.a1,
		tmp_B.b1,
		'c1的默认值',
		tmp_A.a2,
		tmp_B.b2,
	FROM
		( SELECT pkey, a1, a2 FROM A ) tmp_A,
		( SELECT pkey, b1, b2 FROM B ) tmp_B 
	WHERE
		tmp_B.pkey = tmp_A.pkey 
	);