Oracle 18c

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select * from V$VERSION;


BANNER
BANNER_FULL
BANNER_LEGACY
CON_ID


Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
Version 18.4.0.0.0
Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
0


CREATE TABLE TASK_TABLE (
task_num    number(2),
task_date   DATE,
due_date    DATE
);
begin
INSERT INTO TASK_TABLE VALUES (1, '15-SEP-21', NULL);
INSERT INTO TASK_TABLE VALUES (2, '19-SEP-21', NULL);
INSERT INTO TASK_TABLE VALUES (3, '20-SEP-21', NULL);
INSERT INTO TASK_TABLE VALUES (4, '22-SEP-21', NULL);
INSERT INTO TASK_TABLE VALUES (5, '25-SEP-21', NULL);
INSERT INTO TASK_TABLE VALUES (6, '26-SEP-21', NULL);
INSERT INTO TASK_TABLE VALUES (7, '28-SEP-21', NULL);
end;
/
1 rows affected

CREATE TABLE duty_schedule (
day_num NUMBER(3),
duty_date   DATE,
active      NUMBER(1)
);
begin
INSERT INTO duty_schedule VALUES (1,'15-Sep-21',1);
INSERT INTO duty_schedule VALUES (2,'16-Sep-21',0);
INSERT INTO duty_schedule VALUES (3,'17-Sep-21',1);
INSERT INTO duty_schedule VALUES (4,'18-Sep-21',1);
INSERT INTO duty_schedule VALUES (5,'19-Sep-21',0);
INSERT INTO duty_schedule VALUES (6,'20-Sep-21',0);
INSERT INTO duty_schedule VALUES (7,'21-Sep-21',1);
INSERT INTO duty_schedule VALUES (8,'22-Sep-21',1);
INSERT INTO duty_schedule VALUES (9,'23-Sep-21',1);
INSERT INTO duty_schedule VALUES (10,'24-Sep-21',0);
INSERT INTO duty_schedule VALUES (11,'25-Sep-21',1);
INSERT INTO duty_schedule VALUES (12,'26-Sep-21',1);
INSERT INTO duty_schedule VALUES (13,'27-Sep-21',0);
INSERT INTO duty_schedule VALUES (14,'28-Sep-21',1);
INSERT INTO duty_schedule VALUES (15,'29-Sep-21',1);
INSERT INTO duty_schedule VALUES (16,'30-Sep-21',1);
INSERT INTO duty_schedule VALUES (17,'1-Oct-21',1);
INSERT INTO duty_schedule VALUES (18,'2-Oct-21',0);
INSERT INTO duty_schedule VALUES (19,'3-Oct-21',1);
INSERT INTO duty_schedule VALUES (20,'4-Oct-21',0);
INSERT INTO duty_schedule VALUES (21,'5-Oct-21',1);
end;
/
1 rows affected

select
  t.task_num,
  t.task_date,
  d.duty_date
from task_table t
outer apply
(
  select ds.duty_date
  from duty_schedule ds
  where ds.active = 1
  and ds.duty_date > t.task_date
  order by ds.duty_date
  offset 4 rows
  fetch next row only
) d
order by t.task_num;


TASK_NUM
TASK_DATE
DUTY_DATE


1
15-SEP-21
23-SEP-21

2
19-SEP-21
26-SEP-21

3
20-SEP-21
26-SEP-21

4
22-SEP-21
29-SEP-21

5
25-SEP-21
01-OCT-21

6
26-SEP-21
03-OCT-21

7
28-SEP-21
05-OCT-21
TASK_NUM	TASK_DATE	DUTY_DATE
1	15-SEP-21	23-SEP-21
2	19-SEP-21	26-SEP-21
3	20-SEP-21	26-SEP-21
4	22-SEP-21	29-SEP-21
5	25-SEP-21	01-OCT-21
6	26-SEP-21	03-OCT-21
7	28-SEP-21	05-OCT-21