How to make recursive query.Please help

Question

Dear Experts:
I want to retrieve all employees located in a department in addition to all other employees located in the child's nodes of this department too.
Problem Details:
I have "Employees" table and "Departments" Table
The structure of Dept Table is:
ID   primary key
parent_dept   foreign key(id)
deptname  varchar2
deptType varchar2
The Employee table structure is
ID primary key
dept_id foreign key(Department.id)
empName varchar2Sample data for departments
ID : 1
parent_dept : null
deptname: General Manager office
deptType : 'GM'
ID :=2
parent_dept : 1
deptname: Information tech.
deptType : 'DPT'
ID :=3
parent_dept : 2
deptname: Software Development
deptType : 'SECTION'Sample Data for employees
ID : 101
dept_id  :1
empName  King
ID : 102
dept_id  :2
empName  ALAN
ID : 103
dept_id  :2
empName  SAM
ID : 104
dept_id  :3
empName  JANEI want to create a query that accepts a parameter "p_department_id" and returns All employees on the following conditions
1- In case the parameter value is null , then retrieve All Employees "king - alan- sam-jane"
2- In Case the parameter value is 1 , then retrieve all the employees under department id =1 in addition to all the employees located under the children departments.
in this case it will be "king - alan- sam-jane"
3- In case parameter value is 2 , then return all the employees under department id =2 in addition to all the employees located under the children departments.
In this case it will be " alan- sam-jane"
4- In case parameter value is 3 , then return all the employees under department id =3 in addition to all the employees located under the children departments.
in this case it will be only "JANE"
In brief , If I pass any value to the parameter :p_department_id , I want to retrieve all employees located in this department in addition to other employees located in the child's nodes of this department id
I use oracle database 11g release 2
Please help me
Thanks
Edited by: ta**** on Apr 3, 2013 5:56 PM
Edited by: ta**** on Apr 3, 2013 5:58 PM

Answer 1

SQL> variable p_department_id number
SQL> exec :p_department_id := null
PL/SQL procedure successfully completed.
SQL> with employees as (
  2                     select 101 id,1 dept_id,'King' empName from dual union all
  3                     select 102,2,'ALAN' from dual union all
  4                     select 103,2,'SAM' from dual union all
  5                     select 104,3,'JANE' from dual
  6                    ),
  7     departments as (
  8                     select 1 id,null parent_dept,'General Manager office' deptname,'GM' deptType from dual union all
  9                     select 2,1,'Information tech.','DPT' from dual union all
10                     select 3,2,'Software Development','SECTION' from dual
11                    )
12  select  *
13    from  employees
14    where dept_id in (
15                      select  id
16                        from  departments
17                        start with (
18                                       (
19                                            :p_department_id is null
20                                        and
21                                            parent_dept is null
22                                       )
23                                    or
24                                       id = :p_department_id
25                                   )
26                        connect by parent_dept = prior id
27                     )
28  /
        ID    DEPT_ID EMPN
       101          1 King
       102          2 ALAN
       103          2 SAM
       104          3 JANE
SQL> exec :p_department_id := 1
PL/SQL procedure successfully completed.
SQL> /
        ID    DEPT_ID EMPN
       101          1 King
       102          2 ALAN
       103          2 SAM
       104          3 JANE
SQL> exec :p_department_id := 2
PL/SQL procedure successfully completed.
SQL> /
        ID    DEPT_ID EMPN
       102          2 ALAN
       103          2 SAM
       104          3 JANE
SQL> exec :p_department_id := 3
PL/SQL procedure successfully completed.
SQL> /
        ID    DEPT_ID EMPN
       104          3 JANE
SQL> SY.