Split Row into Mulitple Rows based on Value in Quantity Column

Question

I have a test table which contains Product information and a Quantity Column.

 ProdID = 1 Qty = 3

Where the Quantity is greater than 1, I need to generate the extra rows for the Quantity so output will only ever have Qty=1 against ever row:

 ProdID = 1 Qty = 1
 ProdID = 1 Qty = 1
 ProdID = 1 Qty = 1

I'm a bit stumped where to begin, I've thought about trying to add a row then reduce Qty each time but this will be looping, how can this be done as a Set operation... recrusive cte, cross apply, can it be done in tsql?

with cte_test
as
(select a.* from 
(values('01-JAN-19','PROD1','BLUE',10.00, 1)
  ,('01-JAN-19','PROD1','RED',10.00, 1)
  ,('02-JAN-19','PROD1','BLUE',10.00, 2)
  ,('02-JAN-19','PROD2','BLUE',10.00, 1)
  ,('03-JAN-19','PROD1','RED',20.00, 6)
  ,('04-JAN-19','PROD1','BLUE',10.00, 1)
  ,('04-JAN-19','PROD3','BLACK',10.00, 3)
  ,('05-JAN-19','PROD1','BLUE',10.00, 2)
) as a ([Date],[Product],[Colour],[Price],[Qty])
)

select [Date],[Product],[Colour],[Price],[Qty] 
from cte_test

Answer 1

I like recursive CTEs for this purpose:

with cte as (
      select [Date], [Product], [Colour], [Price], [Qty]
      from [TestTable]
      union all
      select [Date], [Product], [Colour], [Price], [Qty] - 1
      from cte
      where Qty > 1
     )
select [Date], [Product], [Colour], [Price], 1 as [Qty]
from cte;

If Qty is greater than 100, you need to add option (maxrecursive 0) .

Answer 2

With a recursive CTE:

declare @maxqty int = (select max(qty) from [TestTable]);
with cte AS (
  select 1 qty
  union all
  select qty + 1 from cte where qty + 1 <= @maxqty
)
select [Date], [Product], [Colour], [Price], 1 as [Qty]
from [TestTable] t inner join cte c
on c.qty <= t.qty
order by [Date], [Product]

See the demo .
Results:

> Date      | Product | Colour | Price | Qty
> :-------- | :------ | :----- | :---- | --:
> 01-JAN-19 | PROD1   | BLUE   | 10.00 |   1
> 01-JAN-19 | PROD1   | RED    | 10.00 |   1
> 02-JAN-19 | PROD1   | BLUE   | 10.00 |   1
> 02-JAN-19 | PROD1   | BLUE   | 10.00 |   1
> 02-JAN-19 | PROD2   | BLUE   | 10.00 |   1
> 03-JAN-19 | PROD1   | RED    | 10.00 |   1
> 03-JAN-19 | PROD1   | RED    | 10.00 |   1
> 03-JAN-19 | PROD1   | RED    | 10.00 |   1
> 03-JAN-19 | PROD1   | RED    | 10.00 |   1
> 03-JAN-19 | PROD1   | RED    | 10.00 |   1
> 03-JAN-19 | PROD1   | RED    | 10.00 |   1
> 04-JAN-19 | PROD1   | BLUE   | 10.00 |   1
> 04-JAN-19 | PROD3   | BLACK  | 10.00 |   1
> 04-JAN-19 | PROD3   | BLACK  | 10.00 |   1
> 04-JAN-19 | PROD3   | BLACK  | 10.00 |   1
> 05-JAN-19 | PROD1   | BLUE   | 10.00 |   1
> 05-JAN-19 | PROD1   | BLUE   | 10.00 |   1