JOB_HISTORY 테이블 데이터 

 

 

 

 

EMPLOYEES 테이블의 데이터 

 

 

 

DEPARTMENTS 가치 표시해줄려고한다 그럼 3 JOIN 해야함 

 

 select J.EMPLOYEE_ID, J.START_DATE , J.END_DATE, E.FIRST_NAME, J.DEPARTMENT_ID , D.DEPARTMENT_NAME 

  FROM EMPLOYEES E RIGHT JOIN JOB_HISTORY J ON E.EMPLOYEE_ID = J.EMPLOYEE_ID LEFT JOIN DEPARTMENTS D ON J.DEPARTMENT_ID = D.DEPARTMENT_ID; 

 

 해석해보면 

EMPYEES  JOB_HISTORY JOB기준으로 조인을  결과값에 DEPARTMENTS조인을 한다전체 기준은 JOB_HISTORY 이다. 

 

 

여기서  

DEPARTMENT 기준으로 바꾸게 되면 

 

 select J.EMPLOYEE_ID, J.START_DATE , J.END_DATE, E.FIRST_NAME, J.DEPARTMENT_ID , D.DEPARTMENT_NAME 

  FROM EMPLOYEES E RIGHT JOIN JOB_HISTORY J ON E.EMPLOYEE_ID = J.EMPLOYEE_ID RIGHT JOIN DEPARTMENTS D ON J.DEPARTMENT_ID = D.DEPARTMENT_ID; 

 

 

총기준은 부서이다. 

 

 


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