Query that selects rows depending on information in other rows?

Question

Hello!
I have this table that contains employment information about persons. Each person can have one or several rows in this table. The problem I have is that some people who have several jobs are a little special in the way that I need to query them. A person that has several jobs can look like this:
PKEY | PERSONID | EMPTYPE | IDNO | STARTDATE | ENDDATE
1 | 730813 | 0 | 1000 | 09-01-01 | 10-01-01
2 | 730813 | 1 | 1000 | 09-05-01 | 09-09-01
3 | 730813 | 0 | 1001 | 05-03-02 | 11-07-02
The person above has 2 active employments, the first one isn't really active since the person has another temporary employment that has replaced it, it's number 2 and it has the same IDNO. The difference is the EMPTYPE, the ordinary employment has number 0 and the temporary employment has the number 1. On row 3 is the persons other active employment with IDNO 1001 and EMPTYPE 0.
This is what I need to do:
I need to do a select that only gives me the rows 2 and 3 when the employment no 2 is seen as active by looking at the dates, when the current date is between the start and end dates. The select needs to give me rows 1 and 3 when the employment no 2 is no longer active, i.e. when the end date has passed.
Trying to sum it up, when there are several rows with the same PERSONID and the same IDNO and the current date is greater or equal to the STARTDATE but less or equal to the ENDDATE give me only the row where the EMPTYPE is 1 and not the one where the EMPTYPE is 0.
Is this possible to do?
Thanks.

Answer 1

Hi,
Sorry, I can't follow what you're saying about dates. It's hard, not knowing what the date format is.
You probably want analytic functions to do this.
For example to chose the row with the higher emptype (when there is a choice):
WITH  got_rnum  AS
    SELECT  pkey, personid, emptype, idno, startdate, enddate
    ,       ROW_NUMBER () OVER (PARTITION BY personid, idno
                                ORDER BY     emptype    DESC
                               )   AS rnum
    FROM    table_x
SELECT    pkey, personid, emptype, idno, startdate, enddate
FROM    got_rnum
WHERE   rnum    = 1
;Whatever your criteria are for deciding which row you want to pick, make an ORDER BY clause in the ROW_NUMBR function that puts that row first.
If you want to include ties for the row chosen, use RANK instead of ROW_NUMBER.
Edited by: Frank Kulash on Aug 15, 2009 11:09 PM