sqlserver get records count repeating - sql-server

Question

I have one doubt in sql server
get records based on installments
Table :productdetails
CREATE TABLE [dbo].[productdetails](
[productid] [int] NULL,
[Productrstartdate] [date] NULL,
[Productenddate] [date] NULL,
[EMIInstallment] [int] NULL
) ON [PRIMARY]
GO
INSERT [dbo].[productdetails] ([productid], [Productrstartdate], [Productenddate], [EMIInstallment]) VALUES (1, CAST(N'2020-10-02' AS Date), CAST(N'2024-10-02' AS Date), 5)
GO
INSERT [dbo].[productdetails] ([productid], [Productrstartdate], [Productenddate], [EMIInstallment]) VALUES (2, CAST(N'2020-02-10' AS Date), CAST(N'2021-02-10' AS Date), 2)
GO
INSERT [dbo].[productdetails] ([productid], [Productrstartdate], [Productenddate], [EMIInstallment]) VALUES (3, CAST(N'2019-01-10' AS Date), CAST(N'2019-01-10' AS Date), 1)
GO
INSERT [dbo].[productdetails] ([productid], [Productrstartdate], [Productenddate], [EMIInstallment]) VALUES (4, CAST(N'2019-01-18' AS Date), CAST(N'2021-01-18' AS Date), 3)
GO
based on above data i want output like below
Productid |Installmentdate |noofinstallmentcount
1 |2020-10-02 |1
1 |2021-10-02 |2
1 |2022-10-02 |3
1 |2023-10-02 |4
1 |2024-10-02 |5
2 |2020-02-10 |1
2 |2021-02-10 |2
3 |2019-01-10 |1
4 |2019-01-18 |1
4 |2020-01-18 |2
4 |2021-01-18 |3
i tried like below :
DECLARE #MINDATE DATE='2019-01-18'
DECLARE #COUNT INT=10
dECLARE #MAXDATE DATE='2024-10-02'
;WITH ABC
AS
(
SELECT productid ,#MINDATE CalendarDate ,1 as id from [dbo].[productdetails]
UNION ALL
SELECT a.productid ,DATEADD(YEAR,1,a.Productrstartdate ), 1 FROM [dbo].[productdetails] a
join [dbo].[productdetails] b on a.productid=b.productid
WHERE #MINDATE <#MAXDATE )
SELECT * FROM ABC
above query not given expected output
could you please tell me how to write query to achive this task in sql server .

Answer 1

You want a tally here. If you're not going to have a value (much) higher than 10, then just a VALUES clause will work:
SELECT pd.productid,
DATEADD(YEAR, V.I, pd.Productrstartdate) AS Installmentdate,
V.I + 1 AS noofinstallmentcount
FROM dbo.productdetails pd
JOIN (VALUES(0),(1),(2),(3),(4),(5),(6),(7),(8),(9))V(I) ON pd.EMIInstallment > V.I;
If you need bigger numbers, just use a bigger tally:
WITH N AS(
SELECT N
FROM (VALUES(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL))N(N)),
Tally AS(
SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) -1 AS I
FROM N N1, N N2, N N3) --1000 rows
SELECT pd.productid,
DATEADD(YEAR, T.I, pd.Productrstartdate) AS Installmentdate,
T.I + 1 AS noofinstallmentcount
FROM dbo.productdetails pd
JOIN Tally T ON pd.EMIInstallment > T.I;

Answer 2

You could create a temp table that mimics the actual productdetails table, then iterate through it, creating an output table that lists the product id with each installment date. Once you have that, you can use ROW_NUMBER() to count the installment numbers. Try this:
SELECT *
INTO #productdetails
FROM productdetails
CREATE TABLE #output (
productid int null
,installmentdate date null)
WHILE (SELECT COUNT(*) FROM #productdetails) > 0
BEGIN
DECLARE #yr int = 0
WHILE (SELECT TOP 1 DATEDIFF(year, DATEADD(year, #yr, Productrstartdate), productenddate) FROM #productdetails) >= 0
BEGIN
INSERT INTO #output (
productid
,installmentdate)
SELECT top 1
productid
,DATEADD(year, #yr, Productrstartdate) installmentdate
FROM #productdetails
SET #yr = #yr + 1
END
DELETE TOP (1) FROM #productdetails
END
SELECT *
,ROW_NUMBER() OVER (PARTITION BY ProductId ORDER BY InstallmentDate asc) NumberOfInstallmentCount
FROM #output
DROP TABLE #output, #productdetails