分步骤的3表外连接：查询所有员工的工作城市
selectemployee_id, city , department_name from( SELECT employee_id, department_name ,d.location_id fromemployees e , departments d
whered.department_id (+)= e.department_id ) a ,locations l
where a.location_id = l.location_id (+) ;
SELECT employee_id, city, department_name
FROM employees e, departments d, locations l
whered.department_id (+)= e.department_idand d.location_id = l.location_id (+);
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