Oracle SQL相关子查询：不是单组组函数

Question

I'm trying to count travels doctors went to and sum how much money tolls cost. I'm using ORACLE XE 11g and SQL Developer. I tried to do that with correlated subquery in SELECT but I'm getting this message:

ORA-00937: not a single-group group function
00937. 00000 -  "not a single-group group function"
*Cause:    
*Action:
Error at Line: 2 Column: 11 

This is query I talked about:

SELECT person.name, person.surname, COUNT(DISTINCT travelID) AS numberoftravels, 
  (SELECT SUM(costs.cost) FROM costs
    JOIN travel ON costs.travelID = travel.travelID
    JOIN person ON travel.personID = person.personID
    JOIN staff ON travel.personID = staff.staffID
    WHERE stafftype = 'Doctor' AND costtype = 'tolls' and staff1.staffID = person.personID  
  ) AS tollscost

FROM travel JOIN person ON person.personID = travel.personID
  JOIN staff staff1 ON staff1.staffID = person.personID

WHERE stafftype = 'Doctor'
GROUP BY person.name, person.surname;

Counting worked just fine before I added subquery. Does anyone understand why I might be having this problem?

Answer 1

您缺少GROUP BY列-personID