how to loop through each row of every group (while doing "group by") in Oracle table - oracle

Question

I have a table like this:
I want to group by the table base on "customer_id" column and calculate "Day-day[0]" column. "Day-day[0]" is "Day" field in every group and "day[0]" is first row of the day in the group. At the same time, I have to calculate total risk which is in following:
This is the table after grouping by:
This is total risk formula:
In fact, I have to loop through each row of every group to calculate total risk.
My sample table is like this:
CREATE TABLE risk_test
(id VARCHAR2 (32) NOT NULL PRIMARY KEY,
customer_id varchar2 (40BYTE),
risk number,
day VARCHAR2(50 BYTE))
insert into risk_test values(1,102,15,1);
insert into risk_test values(2,102,16,1);
insert into risk_test values(3,104,11,1);
insert into risk_test values(4,102,17,2);
insert into risk_test values(5,102,10,2);
insert into risk_test values(6,102,13,3);
insert into risk_test values(7,104,14,2);
insert into risk_test values(8,104,13,2);
insert into risk_test values(9,104,17,1);
insert into risk_test values(10,104,16,2);
The sample answer is like this:
Would you please guide me how I can do this scenario in Oracle database?
Any help is really appreciated.

Answer 1

Using the sample data that was provided, I believe this query should calculate the risks properly:
Query
SELECT o.*,
ROUND (
SUM (day_minus_day0 * risk) OVER (PARTITION BY customer_id)
/ SUM (day_minus_day0) OVER (PARTITION BY customer_id),
5) AS total_risk
FROM (SELECT rt.*, (rt.day - MIN (rt.day) OVER (PARTITION BY customer_id)) + 1 AS day_minus_day0
FROM risk_test rt) o
ORDER BY customer_id, TO_NUMBER (day), TO_NUMBER (id);
Result
ID CUSTOMER_ID RISK DAY DAY_MINUS_DAY0 TOTAL_RISK
_____ ______________ _______ ______ _________________ _____________
1 102 15 1 1 13.77778
2 102 16 1 1 13.77778
4 102 17 2 2 13.77778
5 102 10 2 2 13.77778
6 102 13 3 3 13.77778
3 104 11 1 1 14.25
9 104 17 1 1 14.25
7 104 14 2 2 14.25
8 104 13 2 2 14.25
10 104 16 2 2 14.25

Answer 2

Your total risk calculation just looks like a weighted average to me. That is, the average risk of the rows for each customer, weighted according to the day offset (day-day[0]), so that risks in later days count for more.
To compute that, you need a common table expression to 1st compute the day-weighted risk for each row. Then you can just compute the weighted average by dividing.
The query below illustrates the approach, with comments.
-- This first WITH clause is just sample data. In your database you would
-- get rid of this and replace all references to "input" with your actual
-- table name
with input ( customer_id, risk, day ) AS (
SELECT 1053, 100, 1 FROM DUAL UNION ALL
SELECT 1053, 100, 1 FROM DUAL UNION ALL
SELECT 1053, 100, 2 FROM DUAL UNION ALL
SELECT 1053, 100, 2 FROM DUAL UNION ALL
SELECT 1053, 100, 3 FROM DUAL UNION ALL
SELECT 1054, 200, 1 FROM DUAL UNION ALL
SELECT 1054, 200, 1 FROM DUAL UNION ALL
SELECT 1054, 200, 3 FROM DUAL UNION ALL
SELECT 1054, 200, 3 FROM DUAL UNION ALL
SELECT 1054, 200, 4 FROM DUAL
),
-- This CTE computes the day offset for each row and multiplies by the risk to
-- compute a day-weighted risk.
-- I added +1 to the day_offset, otherwise risks on the 1st day would not contribute
-- to the total risk, which I think is not what you intended(?)
weighted_input AS (
SELECT i.customer_id,
i.risk,
i.day,
i.day - min(i.day) over ( partition by i.customer_id ) + 1 day_offset,
( i.day - min(i.day) over ( partition by i.customer_id ) + 1 ) * i.risk day_weighted_risk
FROM input i )
-- This is the main SELECT clause that gets all the weighted risks and computes
-- the group total risk, which appears the same in every row in each group.
SELECT wi.*,
sum(wi.day_weighted_risk) over ( partition by wi.customer_id ) / sum(wi.day_offset) over ( partition by wi.customer_id ) total_risk
FROM weighted_input wi;
+-------------+------+-----+------------+-------------------+------------+
| CUSTOMER_ID | RISK | DAY | DAY_OFFSET | DAY_WEIGHTED_RISK | TOTAL_RISK |
+-------------+------+-----+------------+-------------------+------------+
| 1053 | 100 | 1 | 1 | 100 | 100 |
| 1053 | 100 | 1 | 1 | 100 | 100 |
| 1053 | 100 | 2 | 2 | 200 | 100 |
| 1053 | 100 | 2 | 2 | 200 | 100 |
| 1053 | 100 | 3 | 3 | 300 | 100 |
| 1054 | 200 | 1 | 1 | 200 | 200 |
| 1054 | 200 | 1 | 1 | 200 | 200 |
| 1054 | 200 | 3 | 3 | 600 | 200 |
| 1054 | 200 | 3 | 3 | 600 | 200 |
| 1054 | 200 | 4 | 4 | 800 | 200 |
+-------------+------+-----+------------+-------------------+------------+
For your database, having the actual table and not needing the input CTE, it would be:
WITH weighted_input AS (
-- This CTE computes the day offset for each row and multiplies by the risk to
-- compute a day-weighted risk.
-- I added +1 to the day_offset, otherwise risks on the 1st day would not contribute
-- to the total risk, which I think is not what you intended(?)
SELECT i.customer_id,
i.risk,
i.day,
i.day - min(i.day) over ( partition by i.customer_id ) + 1 day_offset,
( i.day - min(i.day) over ( partition by i.customer_id ) + 1 ) * i.risk day_weighted_risk
FROM my_table i )
-- This is the main SELECT clause that gets all the weighted risks and computes
-- the group total risk, which appears the same in every row in each group.
SELECT wi.*,
sum(wi.day_weighted_risk) over ( partition by wi.customer_id ) / sum(wi.day_offset) over ( partition by wi.customer_id ) total_risk
FROM weighted_input wi;