Generating multiple data with SQL query - sql

Question

I have 2 tables as below
Product_Asset:
PAId Tracks
1 2
2 3
Product_Asset_Resource:
Id PAId TrackNumber
1 1 1
2 1 2
3 2 1
4 2 2
5 2 3
I would like to know if I can generate the data in product_asset_resource table based on product_asset table using TSQL query (without complex cursor etc.)
For example, if the number of tracks in product_asset is 3 then I need to populate 3 rows in product_asset_resource with track numbers as 1,2,3

Answer 1

You can do this with the help of a Tally Table.
WITH E1(N) AS( -- 10 ^ 1 = 10 rows
SELECT 1 FROM(VALUES (1),(1),(1),(1),(1),(1),(1),(1),(1),(1))t(N)
),
E2(N) AS(SELECT 1 FROM E1 a CROSS JOIN E1 b), -- 10 ^ 2 = 100 rows
E4(N) AS(SELECT 1 FROM E2 a CROSS JOIN E2 b), -- 10 ^ 4 = 10,000 rows
CteTally(N) AS(
SELECT TOP(SELECT MAX(Tracks) FROM Product_Asset)
ROW_NUMBER() OVER(ORDER BY(SELECT NULL))
FROM E4
)
SELECT
Id = ROW_NUMBER() OVER(ORDER BY pa.PAId, t.N),
pa.PAId,
TrackNumber = t.N
FROM Product_Asset pa
INNER JOIN CteTally t
ON t.N <= pa.Tracks
ONLINE DEMO

Answer 2

Try this,I am not using any Tally Table
declare #Product_Asset table(PAId int,Tracks int)
insert into #Product_Asset values (1 ,2),(2, 3)
;with CTE as
(
select PAId,1 TrackNumber from #Product_Asset
union all
select pa.PAId,TrackNumber+1 from #Product_Asset pa
inner join cte c on pa.PAId=c.PAId
where c.TrackNumber<pa.Tracks
)
select ROW_NUMBER()over(order by paid)id, * from cte
IMHO,Recursive CTE or sub query or using temp table performance depend upon example to example.
I find Recursive CTE more readable and won't use them unless they exhibit performance problem.
I am not convince that Recursive CTE is hidden RBAR.
CTE is just syntax so in theory it is just a subquery
We can take any example to prove that using #Temp table will improve the performance ,that doesn't mean we always use temp table.
Similarly in this example using Tally Table may not improve the performance this do not imply that we should take help of Tally Table at all.