Repeat a value over some rows - sql

Question

I have a list of values and I have to display the mother value of the CHILDVALUE in the following way. The MOTHERVALUE should be same as CHILDVALUE at RNO = 1 , Otherwise the MOTHERVALUE is repeated for subsequent rows until a new sequence beginning from RNO = 1 is encountered. Below is what I wish to achieve
RNO ChildValue MotherValue SKIPNO CREATEDDATE
1 345dg 345dg 4 19/9/2018 2:49
2 342sds 345dg 4 19/9/2018 11:53
.
.
.
19 343dfd 345dg 4 6/11/2018 12:40
20 234dfs 345dg 4 6/11/2018 14:56
1 545ert 545ert 4 6/11/2018 15:17
2 543tye 545ert 4 7/11/2018 11:29
.
.
.
9 345cxv 545ert 4 16/11/2018 14:16
1 563mnj 563mnj 5 19/11/2018 2:12
The row numbers are dynamically produced according to the SKIPNO (not distinct) and CREATEDDATE. But I have a problem in displaying the correct MOTHERVALUE for some of the rows
I have tried the below query which best captures at least 50% of the requirement.
select RNO
, CHILDVALUE
, case RNO when 1 then CHILDVALUE
else lag(MOTHERVALUE) over (order by SKIPNO, CreatedDate ASC) end as MOTHERVALUE
, SKIPNO, CreatedDate
from( SELECT (ROW_NUMBER() OVER (PARTITION BY A.SKIPNO
ORDER BY A.SKIPNO, A.CreatedDate ASC) RNO
, A.*
from (select distinct CHILDVALUE
, CHILDVALUE as MOTHERVALUE
, SKIPNO
, CreatedDate
from values ) A
)
)
This query partially gives the expected output but is still far from the actual result as it shows the correct MOTHERVALUE only for the first two rows. The query does not help me to show the correctMOTHERVALUE` for more than second row.
Here is my table:
CREATE TABLE VALUES (
CHILDVALUE VARCHAR2(36),
SKIPNO VARCHAR2(36),
CREATEDDATE DATE)
Pls help.

Answer 1

N.B. I am assuming that your sample data had incorrect skipnos for the second and third groups. My answer uses updated values in its sample data.
You can use the first_value analytic function, rather than lag to achieve your aim, e.g.:
WITH vals AS (SELECT '345dg' childvalue, 4 skipno, to_date('19/09/2018 02:49', 'dd/mm/yyyy hh24:mi') createddate FROM dual UNION ALL
SELECT '342sds' childvalue, 4 skipno, to_date('19/09/2018 11:53', 'dd/mm/yyyy hh24:mi') createddate FROM dual UNION ALL
SELECT '343dfd' childvalue, 4 skipno, to_date('06/11/2018 12:40', 'dd/mm/yyyy hh24:mi') createddate FROM dual UNION ALL
SELECT '234dfs' childvalue, 4 skipno, to_date('06/11/2018 14:56', 'dd/mm/yyyy hh24:mi') createddate FROM dual UNION ALL
SELECT '545ert' childvalue, 5 skipno, to_date('06/11/2018 15:17', 'dd/mm/yyyy hh24:mi') createddate FROM dual UNION ALL
SELECT '543tye' childvalue, 5 skipno, to_date('07/11/2018 11:29', 'dd/mm/yyyy hh24:mi') createddate FROM dual UNION ALL
SELECT '345cxv' childvalue, 5 skipno, to_date('16/11/2018 14:16', 'dd/mm/yyyy hh24:mi') createddate FROM dual UNION ALL
SELECT '563mnj' childvalue, 6 skipno, to_date('19/11/2018 02:12', 'dd/mm/yyyy hh24:mi') createddate FROM dual)
SELECT row_number() OVER (PARTITION BY skipno ORDER BY createddate) rno,
childvalue,
first_value(childvalue) OVER (PARTITION BY skipno ORDER BY createddate) mothervlue,
skipno,
createddate
FROM vals;
RNO CHILDVALUE MOTHERVLUE SKIPNO CREATEDDATE
---------- ---------- ---------- ---------- -----------
1 345dg 345dg 4 19/09/2018
2 342sds 345dg 4 19/09/2018
3 343dfd 345dg 4 06/11/2018
4 234dfs 345dg 4 06/11/2018
1 545ert 545ert 5 06/11/2018
2 543tye 545ert 5 07/11/2018
3 345cxv 545ert 5 16/11/2018
1 563mnj 563mnj 6 19/11/2018