PL/SQL :: Creating Collection And Joining List To Database Table?

based on a provided list of key values, joining the collected list against a source table to retrieve additional information related to the key. In this simple example, the procedure accepts a list of employee numbers. The goal is to print a list of names associated with those numbers.

The method is to materialize the list of employee numbers as rows and join those rows to a source table to get the names. I have used BULK COLLECT. Why we cannot cast PLSQL tables using a type defined in the procedure's specification (why the type needs to exist as an object before we can cast it, like this:

SELECT * FROM TABLE ( CAST ( SOME_FUNCTION(&some parameter) AS SOME_TYPE ) );

here is my demo SQL, which you should be able to execute against the SCOTT schema without any change

declare
type employee_numbers is table of emp.empno%type index by binary_integer;
type employee_names is table of emp.ename%type index by binary_integer;
type employees_record is record (empno employee_numbers, person_name employee_names);
records employees_record;

[code]...