Compute Date Range with SQL Statement

Question

I'm sure there is a way to do this in SQL, but I cannot figure it out. I can write a PL/SQL script to do it, but would prefer using a SQL Statement. My database is Oracle Database 10.2.0.4.0.
I have a table that contains information such as the employee number, department id, and the effective date of when the person started in that department. There is data in another table that I want to update their department number in based on their effective date range. If I could figure out how to select the effective date range correctly, I can do the rest.
I have data such as:
EMP_ID DEPT_NO EFFECTIVE
101 1000 1/15/2001
101 1050 5/24/2005
101 2010 6/8/2008
101 1000 8/2/2010
I want to write a SELECT statement that returns something like this where the END_DATE is the day before the EFFECTIVE date and the last record does not have an END_DATE because they are still assigned to that department. Also, the first record in the column, I don't want to select a DEPT_NO because the effective date logic was added in January 2001 so if a person started back in 1985 they could have switched departments zero to many times so I'm not going to update any data for that period:
EMP_ID DEPT_NO EFFECTIVE END_DATE
101 1/14/2001
101 1000 1/15/2001 5/23/2005
101 1050 5/24/2005 6/7/2008
101 2010 6/8/2008 8/1/2010
101 1000 8/2/2010
Below is a script to create the data in a temp table that can be used to write a SELECT statement on. I have added two employee records with different dates.
create table temp_activity
(emp_id number(12),
dept_no number(12),
effective date);
INSERT INTO temp_activity
(EMP_ID,DEPT_NO,EFFECTIVE)
VALUES
(101,1000,to_date('1/15/2001','MM/DD/YYYY'))
INSERT INTO temp_activity
(EMP_ID,DEPT_NO,EFFECTIVE)
VALUES
(101,1050,to_date('5/24/2005','MM/DD/YYYY'))
INSERT INTO temp_activity
(EMP_ID,DEPT_NO,EFFECTIVE)
VALUES
(101,2010,to_date('6/8/2008','MM/DD/YYYY'))
INSERT INTO temp_activity
(EMP_ID,DEPT_NO,EFFECTIVE)
VALUES
(101,1000,to_date('8/2/2010','MM/DD/YYYY'))
INSERT INTO temp_activity
(EMP_ID,DEPT_NO,EFFECTIVE)
VALUES
(102,1040,to_date('1/15/2001','MM/DD/YYYY'))
INSERT INTO temp_activity
(EMP_ID,DEPT_NO,EFFECTIVE)
VALUES
(102,2000,to_date('6/16/2006','MM/DD/YYYY'))
Any help is appreciated. This is probably easy, but I cannot get my brain wrapped around it.
Thanks - mike

Answer 1

select  emp_id,
        dept_no,
        effective,
        end_date
  from  (
          select  emp_id,
                  dept_no,
                  effective,
                  lead(effective) over(partition by emp_id order by effective) - 1 end_date,
                  row_number() over(partition by emp_id order by effective) rn
            from  temp_activity
         union all
          select  emp_id,
                  null dept_no,
                  null effective,
                  min(effective) - 1 end_date,
                  0 rn
            from  temp_activity
            group by emp_id
  order by emp_id,
           rn
    EMP_ID    DEPT_NO EFFECTIVE  END_DATE
       101                       01/14/2001
       101       1000 01/15/2001 05/23/2005
       101       1050 05/24/2005 06/07/2008
       101       2010 06/08/2008 08/01/2010
       101       1000 08/02/2010
       102                       01/14/2001
       102       1040 01/15/2001 06/15/2006
       102       2000 06/16/2006
8 rows selected.
SQL> SY.