MERGE table，匹配时什么都不做

Question

我在 2 个不同的模式中有一个 table DOMAINS，列为 ID、NAME、CODE、DESCRIPTION。

对于新模式中存在的任何NAME，它应该使用现有的ID而不进行任何合并；对于那些新的 NAME 记录，它应该从旧模式插入 ID。

MERGE INTO DOMAINS A
USING (SELECT ID,NAME,CODE,DESCRIPTION FROM <Old Schema 6.1>.DOMAINS@DB_MIG_61_TO_74) B
ON(A.NAME = B.NAME)
WHEN MATCHED **<do nothing>**
WHEN NOT MATCHED THEN INSERT(A.ID,A.NAME,A.CODE,A.DESCRIPTION) 
VALUES(B.ID,B.NAME,B.CODE,B.DESCRIPTION);

如何解释上述查询中 do nothing 的部分？

Answer 1

对于您的情况，无需使用以下部分：

WHEN MATCHED THEN UPDATE ...

( using WHEN MATCHED THEN UPDATE SET a.id = a.id 被接受（Oracle 不投掷）但是没有影响，所以，这样的用法是多余的，因为你不想为匹配大小写。 )

If you wanted to change, then add

WHEN MATCHED THEN UPDATE SET a.id = b.id

before WHEN NOT MATCHED THEN INSERT...

( e.g.Oracle supports WHEN MATCHED THEN UPDATE syntax. Refer the Demo below )

继续当前案例的以下内容：

SQL> CREATE TABLE domains( 
                           id          INT, 
                           name        VARCHAR2(50), 
                           code        VARCHAR2(50), 
                           description VARCHAR2(50)
                         );

SQL> INSERT INTO domains VALUES(1,'Domain A','D.A.','This is Domain A');

SQL> MERGE INTO domains A USING 
     (SELECT 2 id, 'Domain A' name, 'D.A.' code, 'This is Domain A' description 
        FROM domains) b
          ON ( a.name = b.name )
        WHEN NOT MATCHED THEN INSERT( a.id, a.name, a.code, a.description ) 
                              VALUES( b.id, b.name, b.code, b.description );

SQL> SELECT * FROM domains;

ID  NAME        CODE    DESCRIPTION
--  --------   -----  ----------------
1   Domain A    D.A.  This is Domain A

SQL> DELETE domains;

SQL> INSERT INTO domains VALUES(1,'Domain A','D.A.','This is Domain A');
-- we're deleting and inserting the same row again

SQL> MERGE INTO domains A USING       
 (SELECT 2 id, 'Domain B' name, 'D.B.' code, 'This is Domain B' description 
    FROM domains) b
      ON ( a.name = b.name )
    WHEN NOT MATCHED THEN INSERT( a.id, a.name, a.code, a.description ) 
                          VALUES( b.id, b.name, b.code, b.description );


SQL> SELECT * FROM domains;

ID  NAME        CODE    DESCRIPTION
--  --------   -----  ----------------
1   Domain A    D.A.  This is Domain A
2   Domain B    D.B.  This is Domain B

Demo

Answer 2

Oracle SQL 语法支持没有任何 when matched then update 子句。

drop table ft purge;
create table ft (c1 number, c2 varchar2(10));

drop table ld purge;
create table ld (c1 number, c2 varchar2(10));

insert into ft values (1,'a');
insert into ld values (1,'b');
insert into ld values (2,'c');
commit;

merge into ft 
using ld
on (ft.c1 = ld.c1) 
when not matched then
insert (c1,c2) values (ld.c1,ld.c2);

select * from ft;

C1  C2
--- ---
1   a
2   c

2 rows selected.

Answer 3

为什么不用
合并到 A
使用 B
在...
如果不匹配则
...

我已验证有效...

MERGE table，匹配时什么都不做

MERGE table, do nothing when matched

sql

oracle

merge

match

sql-merge