Oracle - UPSERT with update not performed for unmodified values

Question

I am using the following update or inserting an Oracle statement at the moment:

BEGIN
  UPDATE DSMS
     SET SURNAME = :SURNAME
   WHERE DSM = :DSM;
  IF (SQL%ROWCOUNT = 0) THEN
    INSERT INTO DSMS
      (DSM, SURNAME)
    VALUES
      (:DSM, :SURNAME);
  END IF;
END;

This works fine, except that the update statement performs a dummy update if the data is the same as the parameter values. I would not mind a fictitious update in a normal situation, but there is a replication / synchronization system built on this table using triggers on the tables to collect updated records and frequent execution of this statement for many records just means that I will cause huge traffic in the triggers and the system synchronization.

, , , IF-EXISTS, , , ?

DECLARE
  CNT NUMBER;
BEGIN
  SELECT COUNT(1) INTO CNT FROM DSMS WHERE DSM = :DSM;
  IF SQL%FOUND THEN
    UPDATE DSMS
       SET SURNAME = :SURNAME
     WHERE DSM = :DSM
       AND SURNAME != :SURNAME;
  ELSE
    INSERT INTO DSMS
      (DSM, SURNAME)
    VALUES
      (:DSM, :SURNAME);
  END IF;
END;

---

MERGE INTO, , ( , PK).

MERGE INTO:

CREATE TABLE DSMS(
  dsm VARCHAR2(10) NOT NULL PRIMARY KEY,
  surname VARCHAR2(10) NOT NULL
);
> Table created

-- :DSM = 'xx', :SURNAME = 'xx'
MERGE INTO DSMS D
USING (SELECT :DSM       AS DSM,
              :SURNAME   AS SURNAME
         FROM DUAL) V
ON (D.DSM = V.DSM)
WHEN MATCHED THEN
  UPDATE
     SET SURNAME = V.SURNAME
   WHERE D.SURNAME <> V.SURNAME
WHEN NOT MATCHED THEN
  INSERT (DSM, SURNAME)
  VALUES (V.DSM, V.SURNAME);

> Ok - record inserted

-- :DSM = 'xx', :SURNAME = 'xx'
MERGE INTO DSMS D
USING (SELECT :DSM       AS DSM,
              :SURNAME   AS SURNAME
         FROM DUAL) V
ON (D.DSM = V.DSM)
WHEN MATCHED THEN
  UPDATE
     SET SURNAME = V.SURNAME
   WHERE D.SURNAME <> V.SURNAME
WHEN NOT MATCHED THEN
  INSERT (DSM, SURNAME)
  VALUES (V.DSM, V.SURNAME);

> ORA-00001 - Unique constraint violated (PK violation)

, Oracle UPDATE... IF SQL% ROWCOUNT = 0 THEN INSERT... MERGE INTO? MERGE INTO , INSERT, PK, , .

Answer 1

MERGE
INTO    dsms d
USING   (
        SELECT  :DSM AS dsm, :SURNAME AS surname, :FIRSTNAME AS firstname, :VALID AS valud
        FROM    dual
        ) v
ON      (d.dsm = q.dsm)
WHEN MATCHED THEN
UPDATE
SET     SURNAME = v.SURNAME, FIRSTNAME = v.FIRSTNAME, VALID = v.VALID
WHERE   d.surname <> v.surname
        OR d.firstname <> v.firstname
        OR d.valid <> v.valid
WHEN NOT MATCHED THEN
INSERT
INTO    (SURNAME, FIRSTNAME, VALID)
VALUES  (SURNAME, FIRSTNAME, VALID)

NULL , NULL.

Answer 2

. , , , , .

BEGIN
  INSERT INTO DSMS
      (DSM, SURNAME)
  VALUES
      (:DSM, :SURNAME);
EXCEPTION WHEN DUP_VAL_ON_INDEX THEN
    UPDATE DSMS
       SET SURNAME = :SURNAME
     WHERE DSM = :DSM
       AND SURNAME != :SURNAME;
END;