Oracle - Avoid Inserting Duplicate Rows

 INSERT INTO DEPARTMENT
 (
     ID
    ,DESC
    ,CRT
 )
 SELECT 
    20 as ID ,Human Resources' as DESC, TO_DATE('15.11.2008', 'DD.MM.YYYY') as CRT 
 FROM DUAL WHERE NOT EXISTS (SELECT * FROM DEPARTMENT WHERE DESC = 'Human Resources');

 MERGE INTO DEPARTMENT TRG
 USING (
    select 73 as ID ,'Sales' as DESC, TO_DATE('19.11.2008', 'DD.MM.YYYY') as CRT  from dual  
  ) SRC
 ON ( SRC.DESC = TRG.DESC)
 WHEN NOT MATCHED THEN
     INSERT (
           ID
         , DESC
         , CRT
 ) VALUES (
           SRC.ID
         , SRC.DESC
         , SRC.CRT
 )
 WHEN MATCHED THEN
     UPDATE SET TRG.ID = SRC.ID , TRG.CRT = SRC.CRT
 ;

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