Query to retain latest non-zero value - sql-server

Question

I'm using SQL Server 2016 and have a table with the following data:
PlaySeq
TransMaxValue
1
250
2
500
3
0
4
400
5
0
6
300
7
500
8
0
9
0
I'm trying to construct a query that adds a column TransMaxValueContd to that dataset.
That TransMaxValueContd column should retain the last non-zero value encountered in column TransMaxValue.
Ordering is done by PlaySeq.
My expected result from the query is this:
PlaySeq
TransMaxValue
TransMaxValueContd
1
250
250
2
500
500
3
0
500
4
400
400
5
0
400
6
300
300
7
500
500
8
0
500
9
0
500
I've been using windowing functions like LAST_VALUE() and LAG(), but can't seem to get the results right.
Maybe I'm overcomplicating it.
Does anyone know how to do this?
ps: I'm just looking for the query. No need to modify the source table.
Edit: Added a SQLFiddle example with a failed attempt, which is:
SELECT a.PlaySeq,
a.TransMaxValue,
IIF(ISNULL(LAG(a.TransMaxValue,1) OVER (ORDER BY a.PlaySeq), a.TransMaxValue) = a.TransMaxValue, a.TransMaxValue, LAG(a.TransMaxValue,1) OVER (ORDER BY a.PlaySeq)) AS TransMaxValueContd
FROM myTable AS a;
Edit: Thank you for all the answers, which provided new useful insights!
I ended up using this, inspired by the answer from SteveC.
SELECT a.PlaySeq,
a.TransMaxValue,
(SELECT TOP 1 x.TransMaxValue
FROM myTable AS x
WHERE x.PlaySeq <= a.PlaySeq
AND x.TransMaxValue != 0
ORDER BY x.PlaySeq DESC) AS TransMaxValueContd
FROM myTable AS a;

Answer 1

A simple way could use OUTER APPLY and SELECT TOP(1). Something like this
select m.PlaySeq, m.[TransMaxValue],
case when m.[TransMaxValue]=0
then oa.TransMaxValue
else m.TransMaxValue end TransMaxValueContd
from myTable m
outer apply (select top(1) mm.[TransMaxValue]
from myTable mm
where m.PlaySeq>mm.PlaySeq
and mm.[TransMaxValue]>0
order by mm.PlaySeq desc) oa;
PlaySeq TransMaxValue TransMaxValueContd
1 250 250
2 500 500
3 0 500
4 400 400
5 0 400
6 300 300
7 500 500
8 0 500
9 0 500

Answer 2

Perhaps this will help:
DECLARE #Tab TABLE(PlaySeq INT, TransMaxValue INT)
INSERT #Tab
VALUES(1,250),(2,500),(3,0),(4,400),(5,0)
,(6,300),(7,500),(8,0),(9,0)
SELECT PlaySeq,
TransMaxValue,
FIRST_VALUE(TransMaxValue) OVER(PARTITION BY Grp ORDER BY PlaySeq) AS TransMaxValueContd
FROM (
SELECT
PlaySeq,
TransMaxValue,
SUM(CASE WHEN TransMaxValue = 0 THEN 0 ELSE 1 END) OVER(ORDER BY PlaySeq) AS Grp
FROM #Tab
) AS tbl
ORDER BY PlaySeq

Answer 3

Please try the following solution.
It is based on Windows function ROW_NUMBER() and non-equal relationship clause:
FROM #tbl AS t1 INNER JOIN
#tbl AS t2 ON t1.PlaySeq > t2.PlaySeq
SQL
-- DDL and sample data population, start
DECLARE #tbl TABLE (PlaySeq INT, TransMaxValue INT);
INSERT INTO #tbl (PlaySeq, TransMaxValue) VALUES
(1, 250),
(2, 500),
(3, 0 ),
(4, 400),
(5, 0 ),
(6, 300),
(7, 500),
(8, 0 ),
(9, 0 );
-- DDL and sample data population, end
;WITH rs AS
(
SELECT t1.*
, t2.TransMaxValue AS prev_value
, ROW_NUMBER() OVER (PARTITION BY t1.PlaySeq ORDER BY t2.PlaySeq DESC) AS seq
FROM #tbl AS t1 INNER JOIN
#tbl AS t2 ON t1.PlaySeq > t2.PlaySeq
WHERE t2.TransMaxValue > 0
)
SELECT PlaySeq, TransMaxValue, TransMaxValue AS TransMaxValueContd
FROM #tbl WHERE PlaySeq = 1
UNION ALL
SELECT PlaySeq, TransMaxValue, IIF(TransMaxValue > 0, TransMaxValue, prev_value) AS TransMaxValueContd
FROM rs
WHERE seq = 1
ORDER BY PlaySeq ASC;
Output
+---------+---------------+--------------------+
| PlaySeq | TransMaxValue | TransMaxValueContd |
+---------+---------------+--------------------+
| 1 | 250 | 250 |
| 2 | 500 | 500 |
| 3 | 0 | 500 |
| 4 | 400 | 400 |
| 5 | 0 | 400 |
| 6 | 300 | 300 |
| 7 | 500 | 500 |
| 8 | 0 | 500 |
| 9 | 0 | 500 |
+---------+---------------+--------------------+

Answer 4

There may be a better way, but you could try using correlated subqueries:
SELECT q.PlaySeq, q.TransMaxValue
, (CASE
WHEN q.TransMaxValue <> 0 THEN q.TransMaxValue
ELSE (SELECT d.TransMaxValue FROM myTable d WHERE d.PlaySeq = q.PlaySeqRef)
END) TransMaxValueContd
FROM (
SELECT PlaySeq
, TransMaxValue
, (SELECT MAX(PlaySeq)
FROM myTable b
WHERE b.PlaySeq < a.PlaySeq
AND b.TransMaxValue <> 0) PlaySeqRef
FROM myTable a) q;