Break the algorithm through sql query

Question

Hi,
My table 'x' contains data as follows:
Row_id
Person
Effective_date
Status
Code
1
12345
8-Apr-04
POS
A
2
12345
13-Jun-04
PLA
P
3
12345
20-Oct-04
POS
P
4
12345
1-Apr-05
PAY
P
5
12345
8-Aug-05
RFL
A
6
12345
8-Aug-05
XFR
A
7
12345
1-Apr-05
PAY
P
Need this row as output
8
12345
14-Jul-06
LOA
L
9
12345
1-Oct-06
PAY
P
10
12345
16-Jul-07
LOA
L
11
12345
17-Jul-07
RFL
A
Logic that should be used:
1. Get the most recent row based on effective date and code in L or P-> In this case row 10 since this row has L and is latest one
2. Then go back in time until the code is not in L or P -> so based on above data row 6 since the code is 'A'
3. Then come forward from that record 6 until you get status LOA or PLA -> you will come and stand on row '8'
4. finally i need the row_id = 8 as output based on the above steps
Pls help me in framing a query for this

Answer 1

Your effective dates are not unique, therefore it is impossible to decide which row with same effective date goes first. It is not possible to provide a deterministic solution until you define rules how to order rows with same effective date. Solution below is non-deterministic. Because you have rows with same effective date it can produce different results next time you run it. When you define ordering rules add them to ORDER BY clause of ROW_NUMBER function in below code. This will make it deterministic:
with t1 as (
            select  e.*,
                    row_number() over(partition by emplid order by effective_start_date) rn
              from  employee e
     t2 as (
            select  t1.*,
                    max(
                        case
                          when code in ('L','P') then rn
                        end
                      over(partition by emplid) last_l_p_rn,
                    last_value(
                               case
                                  when code not in ('L','P') then rn
                               end
                               ignore nulls
                      over(partition by emplid order by rn) last_non_l_p_rn,
                    first_value(
                                case
                                   when status in ('LOA','PLA') then rn
                               end
                               ignore nulls
                      over(
                           partition by emplid
                           order by rn
                           rows between current row and unbounded following
                         ) first_loa_pla_rn
              from  t1
select  emplid,
        effective_start_date,
        status,
        code
  from  t2
  where level = 3
  start with rn = last_l_p_rn
  connect by (emplid = prior emplid and rn = prior last_non_l_p_rn and level = 2)
          or (emplid = prior emplid and rn = prior first_loa_pla_rn and level = 3)
EMPLID     EFFECTIVE STA C
12345      14-JUL-06 LOA L
SQL>
SY.