Crystal report - complicated sql query

Question

 

 

I have the above table namely departmentRequisition and departmentRequisitionDetail respectively.

 

From the departmentRequisitionDetail, there is a column - departmentRequisitionId - 112 and many rows of acutalQuanity that I need to add up as a total quantity to display as a pie chart.

 

Now, in order to know the department that ties to this total qauntity, I need to refer to another table - departmentRequisition which shows the deparmentId - 2 which ties to this departmentRequisitionId.

 

 

Can someone advise how should I write the query so that I can generate the pie chart ?

The above is just for one departmentId and I need to have different departmentId showing the acutalquanity which is the quantity they ordered.

 

Or is there a better way to generate my crystal report based on the scenario above ?  Like create another table to make things easier.