126.View the Exhibit and examine the data in the PROJ_TASK_DETAILS table.

126.View the Exhibit and examine the data in the PROJ_TASK_DETAILS table.

The PROJ_TASK_DETAILS table stores information about tasks involved in a project and the relation

between them.

The BASED_ON column indicates dependencies between tasks. Some tasks do not depend on the

completion of any other tasks.

You need to generate a report showing all task IDs, the corresponding task ID they are dependent on, and

the name of the employee in charge of the task it depends on.

Which query would give the required result?



A.SELECT p.task_id, p.based_on, d.task_in_charge

FROM proj_task_details p JOIN proj_task_details d ON (p.based_on = d.task_id);

B.SELECT p.task_id, p.based_on, d.task_in_charge

FROM proj_task_details p LEFT OUTER JOIN proj_task_details d ON (p.based_on = d.task_id);

C.SELECT p.task_id, p.based_on, d.task_in_charge

FROM proj_task_details p FULL OUTER JOIN proj_task_details d ON (p.based_on = d.task_id);

D.SELECT p.task_id, p.based_on, d.task_in_charge

FROM proj_task_details p JOIN proj_task_details d ON (p.task_id = d.task_id);

答案：B

解析：首先应该知道条件应该是p.based_on = d.task_id，排除D，这里based_on可能为null，应此排除

A，c是full join连接，这里比如p02这个taskid，其实没有对应的based_on,但是这里 d.task_in_charge也会显示出来，

这里存在问题，所以排除C