OCP Exam documentation

Question

Dear all,
I'm not sure whether this question is supposed to be published here. Please correct me if I am wrong in this question. I was reading the Oracle OCP SQL exam guide, when I faced a wrong "question" and surprisingly an "answer".
Page 139 question number
6: You develop the following SQL statement containing a group expression. Which line in the following select statement, when removed from the statement will correct the error:
SELECT DEPTNO, AVG(SAL) FROM EMP GROUP BY EMPNO;
A.select deptno, avg(sal).
B.from EMP.
C. group by EMPNO
D. There are no errors in this statement, therfore no clauses should be removed.
What is intersting in this question is that the answer is explained descriptive.
(according to ORacle 9 SQL exam Guide the correct answer is C!
Do you think it's right?
First of all can some one tell me what the correct answer is? Since I'm preparing myself for the OCP exam I would want to share this with you guys. Or if someone would know where is the best place to publish things that concerning exam doc mistakes?
Thanks

Answer 1

this question is not valid. just forget it...
The line which generates the error is the line A.
SQL>  SELECT  DEPTNO, AVG(SAL)
FROM EMP
GROUP BY EMPNO;
SELECT  DEPTNO, AVG(SAL)
ERROR at line 1:ORA-00979: not a GROUP BY expressionBut the question is not "what does generate the error", but which line would "correct" the statement when removed.
In which case, there is no valid answer.
SQL> SELECT DEPTNO, AVG(SAL)
  2  FROM EMP;
SELECT DEPTNO, AVG(SAL)
ERROR at line 1:
ORA-00937: not a single-group group function
SQL> SELECT DEPTNO, AVG(SAL)
  2  GROUP BY EMPNO;
GROUP BY EMPNO
ERROR at line 2:
ORA-00923: FROM keyword not found where expected
SQL> FROM EMP
  2 GROUP BY EMPNO
FROM EMP
ERROR at line 1:
ORA-00900: invalid SQL statementHTH
Laurent