Let's learn Left Outer Join!
LEFT OUTER JOIN (i) HR Manager wants all the employees’ details regardless of whether they have past Job-history or not. If employee has a job-history then manager also wants job-history details. Manager to data analyst: Bring me the details of employees along with the details of their job history if employee has one. Data analyst runs below query to fetch the required data. SELECT * FROM EMPLOYEES E LEFT OUTER JOIN JOB_HISTORY JH ON E.EMPLOYEE_ID= JH.EMPLOYEE_ID; (ii) HR manager wants details of departments regardless of department having manager or not. If department has manager then HR manager also wants the details of manager. Manager to data analyst: Bring me the details of departments along with the details of manager of the department. Data analyst runs below query to fetch the required data. SELECT * FROM DEPARTMENTS D LEFT OUTER JOIN EMPLOYEES E ON D.MANAGER_ID= E.EMPLOYEE_ID;