Sql lead and lag / other option for conditional use

Question

Hi all gurus of SQL
I want to pull previous record and subtract status_date from both the record to find the # number of days.
Create table  temp  (o_id number , r_id number ,status_date date , status varchar2(30));
Sample data
i_id     r_id   status_date     status
33493 308963 16-MAR-12 Incarcerated
33493 308943 26-SEP-11 City/County Jail
33493 306529 15-DEC-09 Active
33493 295327 25-SEP-09 City/County Jail
33493 293630 30-JUL-09 Active
33493 292828 30-JUL-09 Active
33493 292830 30-JUL-09 Active
33493 292826 21-MAY-09 City/County Jail
33493 291854 05-MAY-09 Active
Select  I_ID, status_date, lag (R_ID, 1) over (order by status_date )
from TEMP where I_IDin (33493) and  status_date >='01-NOV-2007
and temp.status='Active';
Logic I am trying to accomplish is find the incarceration status_date and then find the latest active , status_date and subtract those dates.
for example 16-mar-12 minus 15-DEC-09
Thanks for help..
Pls help me brainstorm this..

Answer 1

Hi,
This definetly sounds like a job for analytic functions, but LAG might not be the best choice if you can have multiple 'Incarcerated' rows.  You might be better of with LAST_VALUE or MAX, like this:
WITH  got_prev_active_status_date  AS
    SELECT  temp.*       -- or list whatever columns you need
    ,       MAX ( CASE
                      WHEN  status = 'Active'
                      THEN  status_date
                  END
                ) OVER ( PARTITION BY  i_id     -- Just guessing
                         ORDER BY      status_date
                       )   AS prev_active_status_date
    FROM    temp
    WHERE   status   IN ('Active', 'Incarcerated')
SELECT  p.*       -- or list whatever columns you need
,       status_date - prev_active_status_date   AS days_active
FROM    got_prev_active_status_date
WHERE   status  = 'Incarcerated';
I hope this answers your question.
If not, post a little sample data (CREATE TABLE and INSERT statements, relevant columns only) for all the tables involved, and the results you want from that data.
Point out where the query above is producing the wrong results, and explain, using specific examples, how you get the right results from the given data in those places.
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