SQL-在SUM查询中使用COUNT

Question

OK so here is my Database

Patient(PatID, GName, FName, Suburb, PhNo InsurNo)  
Doctor(DocID, DocName, DocSpec, Cost)  
Appointment(AppID, AppTimeDate, PatID*, DocID*)  
Meds(MedID, MedName, Purpose, Admin, AppID*)  
Tests(TestID, TestName, TestResult, TestDate, PatID*)  
DocPat(PatID*, DocID*)  

I am being asked to show the doctors name with the total cost of all appointments greater than average.

so far I have:

SELECT d.DocName, sum((NO_OF_APPS)*DocCost)    
from doctor d, (select count(AppID) as NO_OF_APPS  
                from appointment  
                group by DocID)  
group by DocName;

trying to use sum(count(appID)*DocCost) i know i am coming at this from the wrong angle can anyone shed some light?

Have made corrective adjustments:

SELECT d.DocName, d.docCost*COUNT(ap.AppID) as totalCost  
from doctor d  
left join appointment ap on ap.DocID=d.DocID  
GROUP BY d.DocID  
ORDER BY d.DocName  
HAVING totalCost > AVG(totalCost);

receiving '00933. 00000 - "SQL command not properly ended' on Oracle SQL developer V4

Answer 1

Use join instead of subselects, it is much clearer and usually works faster. To analyze aggregation results you can use HAVING clause. Here is an example:

SELECT d.DocName, d.Cost*COUNT(a.AppID) as totalCost
from doctor d
left join appointment a on a.DocID=d.DocID
GROUP BY d.DocName
HAVING d.Cost > average(d.Cost);
ORDER BY d.DocName