머지를 처음보는 초보입니다..

전체적인 순서가 어떻게 진행되는건지 궁금합니다..

흐름만 알려주시면 큰 도움이 될거같습니다^^

MERGE INTO X_MILEAGE A            
    USING DUAL                           
       ON ( A.MBER_NO = ? ) 

     WHEN MATCHED    THEN                
          UPDATE  SET                    
                  A.ACCML_MILEAGE    = A.ACCML_MILEAGE + (SELECT MILEAGE FROM T_MILEAGE WHERE MILEAGE_ID = ? ),     
                  A.UPDATE_DT = SYSDATE

     WHEN NOT MATCHED THEN               
          INSERT (                       
                 MBER_NO,

        ) VALUES ( ?, 'INET', 'M',
          (SELECT MILEAGE FROM T_MILEAGE WHERE MILEAGE_ID = ?)