Need SQL query using View - Please help

Question

Hi,
I have similar requirement like below.
I have two tables DEPT and EMP and some departments may not have employees. I have created below view, which displays all DEPT records, even though there are no emplyees.
CREATE OR REPLACE VIEW dept_emp_vw AS
SELECT deptno, empid, 0 AS selected
FROM dept d, emp e
WHERE d.deptno = e.deptnno (+);
Ex.
DEPTNO         EMPID        SELECTED
10 101 0
10 102 0
20 103 0
30 103 0
40 104 0
50 <null> 0
Application will pass "empid" to the view (for ex. empid = 103) and I want result like below.
Ex.
DEPTNO         EMPID        SELECTED
10 101 0
10 102 0
20 103 1
30 103 1
40 104 0
50 <null> 0
Can you please let me know the query using "dept_emp_vw" view. We have Oracle 11g Release 2.
Thanks a lot for the help.

Answer 1

Not possible using normal SQL - as SQL is not a procedure language and does not support variable declaration and use (e.g. passing empid as a variable and using it both as a predicate and as a condition in the SQL projection).
That said - SQL can be "+parameterised+". An approach that is ugly and contrary to the basic design and use of SQL. But it can support the (very weird) view definition of yours.
E.g.
SQL> create or replace procedure SetVariable( name varchar2, value varchar2 ) is
  2  begin
  3          DBMS_SESSION.set_context( 'MyVariables', name, value );
  4  end;
  5  /
Procedure created.
SQL>
SQL>
SQL> create or replace context MyVariables using SetVariable;
Context created.
SQL>
SQL> create or replace view my_funky_weird_view as
  2  select
  3          e.empno,
  4          e.ename,
  5          e.job,
  6          case e.empno
  7                  when to_number(sys_context( 'MyVariables', 'empid' )) then
  8                          0
  9                  else
10                          1
11          end     as "SELECTED"
12  from       emp e
13  /
View created.
SQL>
SQL> exec SetVariable( 'empid', 7499 )
PL/SQL procedure successfully completed.
SQL>
SQL> select * from session_context where namespace = 'MYVARIABLES';
NAMESPACE            ATTRIBUTE            VALUE
MYVARIABLES          EMPID                7499
SQL>
SQL> select * from my_funky_weird_view order by selected;
     EMPNO ENAME      JOB               SELECTED
      7499 ALLEN      SALESMAN                 0
      7521 WARD       SALESMAN                 1
      7566 JONES      MANAGER                  1
      7654 MARTIN     SALESMAN                 1
      7698 BLAKE      MANAGER                  1
      7934 MILLER     CLERK                    1
      7788 SCOTT      ANALYST                  1
      7839 KING       PRESIDENT                1
      7844 TURNER     SALESMAN                 1
      7876 ADAMS      CLERK                    1
      7900 JAMES      CLERK                    1
      7902 FORD       ANALYST                  1
      7369 SMITH      CLERK                    1
      7782 CLARK      MANAGER                  1
14 rows selected.
SQL>But I will N\OT recommend doing it this way. It is not natural SQL as PL/SQL is needed to "+inject+" name-value pairs into the context for the SQL view to use. It is ugly. It is not standard. It cannot scale. It is complex to use. Etc.
Yes, there are instances when this approach is exactly what one needs - when for example dealing with a trusted context and using the contents for implementing a security layer. But in the above case - I would rather want to see the actual business requirement first, as I think you're barking up the wrong tree with the view solution you have imagined.