oracle sql to retrieve followup dates from a preceding date - oracle

Question

CREATE TABLE tst_tbl
(
id NUMBER,
last_name VARCHAR2 (50),
first_name VARCHAR2 (50),
dob DATE,
register_dt DATE,
register_loc VARCHAR2 (50),
visit_dt DATE,
visit_loc VARCHAR2 (50),
visit_comments VARCHAR2 (30)
);
INSERT INTO tst_tbl VALUES(1234, 'John', 'Smith', to_date('12/01/1980','MM/DD/YYYY') , to_date('09/05/2017' ,'MM/DD/YYYY') ,'NEW YORK', to_date('02/26/2018','MM/DD/YYYY'), 'NEW JERSEY', '');
INSERT INTO tst_tbl VALUES(1234, 'John', 'Smith', to_date('12/01/1980','MM/DD/YYYY') , to_date('09/05/2017' ,'MM/DD/YYYY') ,'NEW YORK', to_date('2/12/2018', 'MM/DD/YYYY'),'NEW JERSEY', '');
INSERT INTO tst_tbl VALUES(1234, 'John', 'Smith', to_date('12/01/1980','MM/DD/YYYY') , to_date('09/05/2017' ,'MM/DD/YYYY') ,'NEW YORK', to_date('11/6/2017', 'MM/DD/YYYY'),'NEW JERSEY', '');
INSERT INTO tst_tbl VALUES(1234, 'John', 'Smith', to_date('12/01/1980','MM/DD/YYYY') , to_date('09/05/2017' ,'MM/DD/YYYY') ,'NEW YORK', to_date('10/23/2017','MM/DD/YYYY'), 'NEW JERSEY', '');
INSERT INTO tst_tbl VALUES(1234, 'John', 'Smith', to_date('12/01/1980','MM/DD/YYYY') , to_date('09/05/2017' ,'MM/DD/YYYY') ,'NEW YORK', to_date('3/27/2018', 'MM/DD/YYYY'),'NEW JERSEY', '');
INSERT INTO tst_tbl VALUES(1234, 'John', 'Smith', to_date('12/01/1980','MM/DD/YYYY') , to_date('09/05/2017' ,'MM/DD/YYYY') ,'NEW YORK', to_date('3/19/2018', 'MM/DD/YYYY'),'NEW JERSEY', '');
INSERT INTO tst_tbl VALUES(1234, 'John', 'Smith', to_date('12/01/1980','MM/DD/YYYY') , to_date('09/05/2017' ,'MM/DD/YYYY') ,'NEW YORK', to_date('9/11/2017', 'MM/DD/YYYY'),'NEW JERSEY', '');
INSERT INTO tst_tbl VALUES(1234, 'John', 'Smith', to_date('12/01/1980','MM/DD/YYYY') , to_date('2/7/2018' ,'MM/DD/YYYY') , 'NEW YORK',to_date('11/6/2017 ','MM/DD/YYYY'), 'NEW JERSEY', '');
INSERT INTO tst_tbl VALUES(1234, 'John', 'Smith', to_date('12/01/1980','MM/DD/YYYY') , to_date('2/7/2018' ,'MM/DD/YYYY') , 'NEW YORK',to_date('3/19/2018', 'MM/DD/YYYY'),'NEW JERSEY', '');
INSERT INTO tst_tbl VALUES(1234, 'John', 'Smith', to_date('12/01/1980','MM/DD/YYYY') , to_date('2/7/2018' ,'MM/DD/YYYY') , 'NEW YORK',to_date('9/11/2017', 'MM/DD/YYYY'),'NEW JERSEY', '');
INSERT INTO tst_tbl VALUES(1234, 'John', 'Smith', to_date('12/01/1980','MM/DD/YYYY') , to_date('2/7/2018' ,'MM/DD/YYYY') , 'NEW YORK',to_date('3/27/2018', 'MM/DD/YYYY'),'NEW JERSEY', '');
INSERT INTO tst_tbl VALUES(1234, 'John', 'Smith', to_date('12/01/1980','MM/DD/YYYY') , to_date('2/7/2018' ,'MM/DD/YYYY') , 'NEW YORK',to_date('2/26/2018', 'MM/DD/YYYY'),'NEW JERSEY', '');
INSERT INTO tst_tbl VALUES(1234, 'John', 'Smith', to_date('12/01/1980','MM/DD/YYYY') , to_date('2/7/2018' ,'MM/DD/YYYY') , 'NEW YORK',to_date('10/23/2017','MM/DD/YYYY'), 'NEW JERSEY', '');
INSERT INTO tst_tbl VALUES(1234, 'John', 'Smith', to_date('12/01/1980','MM/DD/YYYY') , to_date('2/7/2018' ,'MM/DD/YYYY') , 'NEW YORK',to_date('2/12/2018', 'MM/DD/YYYY'),'NEW JERSEY', '');
COMMIT;
I want immediate visit information(visit_dt, visit_loc, ..) following a register date.
eg:
1234, John, Smith, 12/01/1980, 09/05/2017, NEW YORK, 9/11/2017, NEW JERSEY
1234, John, Smith, 12/01/1980, 2/7/2018, NEW YORK, 2/12/2018, NEW JERSEY
I tried with the below logic to sort the register dates and visit dates and then use lead to retrieve the following date and filter only for register dates. But, i am unable to add other fields as shown above..
SELECT
dt, vst_type, register_dt, vst_dt
FROM
(
SELECT
id, dt, vst_type,
dt AS register_dt,
ROW_NUMBER () OVER
(
PARTITION BY id, dt ORDER BY
CASE
WHEN vst_type = 'REGISTER_DT' THEN 1 ELSE 2 END
)
AS vst_dt_rnum,
LEAD(dt) OVER (PARTITION BY id ORDER BY dt) AS vst_dt
FROM
(
SELECT id, register_dt AS dt, 'REGISTER_DT' vst_type FROM tst_tbl
UNION
SELECT id, visit_dt AS dt, 'VISIT_DT' vst_type FROM tst_tbl
)
)
WHERE vst_dt_rnum = 1 AND vst_type = 'REGISTER_DT'

Answer 1

If I understand correctly, and assuming that the ID is a unique identifier, you want to group the rows by (ID, REGISTER_DT) and from each group to keep just the rows with VISIT_DT >= REGISTER_DT, and then from each group select the earliest (oldest) row by VISIT_DT. If so, something like this should work:
select (columns you want)
from (
select t.*
, row_number() over (partition by id, register_dt
order by visit_dt) as rn
from tst_tbl t
where visit_dt >= register_dt
)
where rn = 1
;

Answer 2

I feel like you're overcomplicating things. Here's a way you can add an indicator if the visit date follows the register date by <30 days. If there's some reason this doesn't work for you, please edit your question and add more data (e.g. what should the output look like?)
select r.*,
case when (floor(visit_dt - register_dt) between 0 and 29)
then 'Y' else 'N'
end as less_than_30_days
from tst_tbl r;
But that's based on your sample output. Based on your query, it looks like you're trying to look for all visits which have any register date within the past 30 days (for that ID). If you'd prefer that instead, here's a simpler way to do it.
select v.*,
(select nvl(max('Y'),'N')
from tst_tbl r
where r.id = v.id
and (floor(v.visit_dt - r.register_dt) between 0 and 29))
as reg_within_30_days
from tst_tbl v;

Answer 3

Try this
Select id, last_name, first_name, dob, register_dt, register_loc,
visit_dt
From (
Select r.id, r.last_name, r.first_name, r.dob, r.register_dt, r.register_loc,
r.visit_dt, r.visit_loc, row_number() over (partition by r.register_dt order by r.visit_dt) r
From tst_tbl r
where register_dt < visit_dt
) x
Where x.r = 1