Question on using CAST, MULTISET and TABLE

Question

Hi,
I am trying to do something that is utterly meaningless, but I am studying the use of CAST with MULTISET and TABLE.
I have created a type: a Nested Table of Number values:
create type numTable as table of number;
Now I perform the following query:
select d.dname
, ( select avg(column_value)
from table
( cast( d.salaries as numTable)
) Department_Avg_Salary
from ( select cast
( multiset
( select e.sal
from emp e
where e.deptno = d1.deptno
) as numTable
) salaries
, d1.dname
from dept d1
) d
I had expected to see each department name and the average salary within that department. Instead, I see the same Department_Avg_Salary value for each row - the average of the first department:
DNAME DEPARTMENT_AVG_SALARY
ACCOUNTING 1875
RESEARCH 1875
SALES 1875
OPERATIONS 1875
However, when I change the query to the following:
select d.dname
, d.salaries
from ( select cast
( multiset
( select e.sal
from emp e
where e.deptno = d1.deptno
) as numTable
) salaries
, d1.dname
from dept d1
) d
I get the following result - note that each department shows the correct list of salaries, not the list of the 1st department's salaries over and over.
DNAME
SALARIES
---------------------------------------------------------ACCOUNTING
NUMTABLE(2450, 1300)
RESEARCH
NUMTABLE(800, 2975, 3000, 5000, 1100, 3000)
SALES
NUMTABLE(1600, 1250, 1250, 2850, 1500, 950)
OPERATIONS
NUMTABLE()
Can someone explain why the
, ( select avg(column_value)
from table
( cast( d.salaries as numTable)
) Department_Avg_Salary
does not give an average per department but instead only the first department's average?
thanks for your help!
regards
Lucas Jellema

Answer 1

scott@ORA92> select d.dname,
  2           (select avg(column_value)
  3            from   table (cast (d.salaries as numTable))
  4            where d.dname = dname) Department_Avg_Salary
  5  from   (select cast (multiset (select e.sal
  6                          from   emp e
  7                          where  e.deptno = d1.deptno) as numTable) salaries,
  8                 d1.dname
  9            from    dept d1) d
10  /
DNAME          DEPARTMENT_AVG_SALARY
ACCOUNTING                2916.66667
RESEARCH                        2175
SALES                     1566.66667
OPERATIONS