UPSERT操作在表中更新或插入一行,这取决于表中是否已经有与数据匹配的行:

if table t has a row exists that has key X:
    update t set mystuff... where mykey=X
else
    insert into t mystuff...

既然Oracle没有特定的UPSERT语句,那么最好的方法是什么呢?


当前回答

我想要Grommit的答案,除了它需要欺骗的值。我在可能出现一次的地方找到了解决方案:http://forums.devshed.com/showpost.php?p=1182653&postcount=2

MERGE INTO KBS.NUFUS_MUHTARLIK B
USING (
    SELECT '028-01' CILT, '25' SAYFA, '6' KUTUK, '46603404838' MERNIS_NO
    FROM DUAL
) E
ON (B.MERNIS_NO = E.MERNIS_NO)
WHEN MATCHED THEN
    UPDATE SET B.CILT = E.CILT, B.SAYFA = E.SAYFA, B.KUTUK = E.KUTUK
WHEN NOT MATCHED THEN
    INSERT (  CILT,   SAYFA,   KUTUK,   MERNIS_NO)
    VALUES (E.CILT, E.SAYFA, E.KUTUK, E.MERNIS_NO); 

其他回答

上面在PL/SQL中的双重示例很棒,因为我想做一些类似的事情,但我想在客户端……所以这里是SQL我用来发送一个类似的语句直接从一些c#

MERGE INTO Employee USING dual ON ( "id"=2097153 )
WHEN MATCHED THEN UPDATE SET "last"="smith" , "name"="john"
WHEN NOT MATCHED THEN INSERT ("id","last","name") 
    VALUES ( 2097153,"smith", "john" )

然而,从c#的角度来看,这比执行更新和查看受影响的行是否为0以及如果为0则执行插入要慢。

没有异常检查的另一种方法:

UPDATE tablename
    SET val1 = in_val1,
        val2 = in_val2
    WHERE val3 = in_val3;

IF ( sql%rowcount = 0 )
    THEN
    INSERT INTO tablename
        VALUES (in_val1, in_val2, in_val3);
END IF;

正如Tim Sylvester的评论所指出的那样,到目前为止给出的答案在并发访问面前都是不安全的,并且在竞争的情况下会引发异常。为了解决这个问题,必须将插入/更新组合包装在某种循环语句中,以便在出现异常时重新执行整个操作。

举个例子,下面是Grommit的代码如何被包装在一个循环中,以使其在并发运行时安全:

PROCEDURE MyProc (
 ...
) IS
BEGIN
 LOOP
  BEGIN
    MERGE INTO Employee USING dual ON ( "id"=2097153 )
      WHEN MATCHED THEN UPDATE SET "last"="smith" , "name"="john"
      WHEN NOT MATCHED THEN INSERT ("id","last","name") 
        VALUES ( 2097153,"smith", "john" );
    EXIT; -- success? -> exit loop
  EXCEPTION
    WHEN NO_DATA_FOUND THEN -- the entry was concurrently deleted
      NULL; -- exception? -> no op, i.e. continue looping
    WHEN DUP_VAL_ON_INDEX THEN -- an entry was concurrently inserted
      NULL; -- exception? -> no op, i.e. continue looping
  END;
 END LOOP;
END; 

注意:在SERIALIZABLE事务模式下,顺便说一句,我不推荐这种模式,你可能会遇到 ORA-08177:不能序列化此事务异常的访问。

MERGE(“老式的方式”)的替代方案:

begin
   insert into t (mykey, mystuff) 
      values ('X', 123);
exception
   when dup_val_on_index then
      update t 
      set    mystuff = 123 
      where  mykey = 'X';
end;   

从http://www.praetoriate.com/oracle_tips_upserts.htm:

在Oracle9i中,UPSERT可以在一条语句中完成这个任务:

INSERT
FIRST WHEN
   credit_limit >=100000
THEN INTO
   rich_customers
VALUES(cust_id,cust_credit_limit)
   INTO customers
ELSE
   INTO customers SELECT * FROM new_customers;