intersection across date ranges from multiple rows in oracle

Intersection of date ranges across rows in oracle.

I have a table which contains following records

We need to find common dates between rule ids

Output will be

I tried with connect by level to generate dates and then take intersection, but it is running for long time due to 9999-12-31

From Oracle 12, you can UNPIVOT the dates and then use analytic functions and MATCH_RECOGNIZE to process the result set row-by-row to find the consecutive rows where both rules are active:

SELECT *
FROM   (
  SELECT item_no,
         item_type,
         rule_id,
         dt,
         SUM(CASE rule_id WHEN 'rule1' THEN active END) OVER (
           PARTITION BY item_no, item_type ORDER BY dt, ACTIVE DESC
         ) AS rule1,
         SUM(CASE rule_id WHEN 'rule2' THEN active END) OVER (
           PARTITION BY item_no, item_type ORDER BY dt, ACTIVE DESC
         ) AS rule2
  FROM   table_name
         UNPIVOT (
           dt FOR active IN ( active_from AS 1, active_to AS -1 )
         )
)
MATCH_RECOGNIZE(
  PARTITION BY item_no, item_type
  ORDER BY dt, rule1 DESC, rule2 DESC
  MEASURES
    FIRST(dt) AS active_from,
    NEXT(dt) AS active_to
  PATTERN ( active_rules+ )
  DEFINE active_rules AS rule1 > 0 AND rule2 > 0
)

Which, for the sample data:

CREATE TABLE table_name (Item_no, item_type, active_from, active_to, rule_id) AS
SELECT 10001, 'SAR', DATE '2020-01-01', DATE '2023-01-01', 'rule1' FROM DUAL UNION ALL
SELECT 10001, 'SAR', DATE '2024-01-01', DATE '9999-12-31', 'rule1' FROM DUAL UNION ALL
SELECT 10001, 'SAR', DATE '2020-05-01', DATE '2021-06-01', 'rule2' FROM DUAL UNION ALL
SELECT 10001, 'SAR', DATE '2021-01-01', DATE '2021-02-01', 'rule2' FROM DUAL;

Outputs:

and for:

CREATE TABLE table_name (Item_no, item_type, active_from, active_to, rule_id) AS
SELECT 10001, 'SPR', DATE '2023-01-01', DATE '2023-01-31', 'rule1' FROM DUAL UNION ALL
SELECT 10001, 'SPR', DATE '2023-01-31', DATE '2023-02-27', 'rule2' FROM DUAL;

The output is:

fiddle

You are looking for overlapping date ranges for the same item, but a different rule.

When do two date ranges A and B overlap? Answer: when the start(B) <= end(A) AND end(B) >= start(A). With this knowledge we can join. The overlapping range is just the greater start date until the lesser end date.

select
  a.item_no,
  a.item_type,
  greatest(a.active_from, b.active_from) as active_from,
  least(a.active_to, b.active_to) as active_to
from mytable a
join mytable b on b.item_no      =   a.item_no
              and b.item_type    =   a.item_type
              and b.rule         <>  a.rule
              and b.active_from  <=  a.active_to
              and b.active_to    >=  a.active_from;