How to display Area wise Data for the following Problem statement? - sql

Question

I have following table structure
Area Section Carrying_Engine
A1 S1 Petrol
A2 S1 Petrol
A3 S1 Diesel
A4 S1 Petrol
A5 S2 Diesel
A6 S2 Petrol
Problem statement is we have to display in how much area Under Section S1 and S2 , Engine carried was Petrol and Diesel , Output has to be
Section From_Area To_Area Carrying_Engine
S1 A1 A3 Petrol
S1 A3 A4 Diesel
S1 A4 A5 Petrol
S2 A5 A6 Diesel
PS : Wherever we have a transition in Either Carrying Engine or Section , the carrying Cost is added into account of the previous Section or Carrying Engine account , for instance ,there is a transition in 3rd row , so here while we move from A2 to A3 , we have used Petrol engine and at A3 point we attach Diesel engine and so in Section S1 , we moved Petrol engine from Area A1 to A3 .
Likewise, in 4-5th row , we move from Section S1 to S2 using Petrol Engine and attached Diesel engine at A5 point but here we add the carrying cost into Section S1 Account only , so from area A4 to A5 , we have used petrol engine in Section S1 .
I am unable to get the logic to solve this ,please guide .

Answer 1

You can take advantage of the analytical function but I must say that you must have some column to identify the order of the column as oracle does not provide automatic ordering of the records.
I have used DATETIME column to identify the order of the column in the following solution:
SQL> WITH YOUR_TABLE (Area, Section, Carrying_Engine, DATETIME) AS
2 (SELECT 'A1', 'S1', 'Petrol', SYSDATE - 6 FROM DUAL UNION ALL
3 SELECT 'A2', 'S1', 'Petrol', SYSDATE - 5 FROM DUAL UNION ALL
4 SELECT 'A3', 'S1', 'Diesel', SYSDATE - 4 FROM DUAL UNION ALL
5 SELECT 'A4', 'S1', 'Petrol', SYSDATE - 3 FROM DUAL UNION ALL
6 SELECT 'A5', 'S2', 'Diesel', SYSDATE - 2 FROM DUAL UNION ALL
7 SELECT 'A6', 'S2', 'Petrol', SYSDATE - 1 FROM DUAL)
8 SELECT * -- your query starts from here
9 FROM
10 (
11 SELECT
12 SECTION,
13 AREA AS FROM_AREA,
14 LEAD(AREA) OVER(ORDER BY DATETIME ) AS TO_AREA,
15 CARRYING_ENGINE
16 FROM
17 (
18 SELECT
19 T.*,
20 LAG(CARRYING_ENGINE) OVER(ORDER BY DATETIME) AS LEAD_CARRYING_ENGINE
21 FROM YOUR_TABLE T
22 )
23 WHERE LEAD_CARRYING_ENGINE <> CARRYING_ENGINE
24 OR LEAD_CARRYING_ENGINE IS NULL
25 )
26 WHERE TO_AREA IS NOT NULL;
SECTION | FROM_AREA | TO_AREA | CARRYING_ENGINE
------- | --------- | ------- | ---------------
S1 | A1 | A3 | Petrol
S1 | A3 | A4 | Diesel
S1 | A4 | A5 | Petrol
S2 | A5 | A6 | Diesel
Cheers!!

Answer 2

Whenever section or engine changes mark row with flag 1, otherwise 0.
case when lag(carrying_engine) over (order by area) = carrying_engine
and lag(section) over (order by area) = section
then 0 else 1 end as flag
Then sum these flags in order.
sum(flag) over (order by a) grp
This will assign each row to group. Now easy, find min area, and min area from next row.
min(a) a1, lead(min(a)) over (order by grp) a2
You can remove last row which you don't want, using
where a2 is not null
Together:
with
groups as (
select a, s, e, sum(flag) over (order by a) grp
from (
select area a, Section s, Carrying_Engine e,
case when lag(carrying_engine) over (order by area) = carrying_engine
and lag(section) over (order by area) = section
then 0 else 1 end as flag
from engines))
select *
from (
select s, e, grp, min(a) a1, lead(min(a)) over (order by grp) a2
from groups group by s, e, grp )
where a2 is not null
order by grp
dbfiddle
I used area to determine order of rows, because it's all you provided, but if your table contains other id use it in order by clauses.