SQL to get a row for start and end date for each year given a start date and number of years - sql

Question

I have the following data in a SQL table:
+------------------------------------+
| ID YEARS START_DATE |
+------------------------------------+
| ----------- ----------- ---------- |
| 1 5 2020-12-01 |
| 2 8 2020-12-01 |
+------------------------------------+
Trying to create a SQL that would expand the above data and give me a start and end date for each year depending on YEARS and START_DATE from above table. Sample output below:
+-----------------------------------------------+
| ID YEAR DATE_START DATE_END |
+-----------------------------------------------+
| ----------- ----------- ---------- ---------- |
| 1 1 2020-12-01 2021-11-30 |
| 1 2 2021-12-01 2022-11-30 |
| 1 3 2022-12-01 2023-11-30 |
| 1 4 2023-12-01 2024-11-30 |
| 1 5 2024-12-01 2025-11-30 |
| 2 1 2020-12-01 2021-11-30 |
| 2 2 2021-12-01 2022-11-30 |
| 2 3 2022-12-01 2023-11-30 |
| 2 4 2023-12-01 2024-11-30 |
| 2 5 2024-12-01 2025-11-30 |
| 2 6 2025-12-01 2026-11-30 |
| 2 7 2026-12-01 2027-11-30 |
| 2 8 2027-12-01 2028-11-30 |
+-----------------------------------------------+

Answer 1

I would use an inline tally for this, as they are Far faster than a recursive CTE solution. Assuming you have low values for Years:
WITH YourTable AS(
SELECT *
FROM (VALUES(1,5,CONVERT(date,'20201201')),
(2,8,CONVERT(date,'20201201')))V(ID,Years, StartDate))
SELECT ID,
V.I + 1 AS [Year],
DATEADD(YEAR, V.I, YT.StartDate) AS StartDate,
DATEADD(DAY, -1, DATEADD(YEAR, V.I+1, YT.StartDate)) AS EndDate
FROM YourTable YT
JOIN (VALUES(0),(1),(2),(3),(4),(5),(6),(7),(8),(9),(10))V(I) ON YT.Years > V.I;
If you have more than 10~ years you can use either create a tally table, or create an large one inline in a CTE. This would start as:
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 --remove the -1 if you don't want to start from 0
FROM N N1, N N2) --100 rows, add more Ns for more rows
...
Of course, I doubt you have 1,000 of years of data.

Answer 2

You can use a recursive CTE:
with cte as (
select id, 1 as year, start_date,
dateadd(day, -1, dateadd(year, 1, start_date)) as end_date,
years as num_years
from t
union all
select id, year + 1, dateadd(year, 1, start_date),
dateadd(day, -1, dateadd(year, 1, start_date)) as end_date,
num_years
from cte
where year < num_years
)
select id, year, start_date, end_date
from cte;
Here is a db<>fiddle.

Answer 3

In a query, you can use the following:
DATEADD(YEAR, 1, DATE_START) - 1
to add this to the table you can just create the extra column, and set it equal to the value of the above, e.g.
UPDATE MyTable
SET DATE_END = DATEADD(YEAR, 1, DATE_START) - 1

Answer 4

If you are working with sql server, then you can try to use operator CROSS APPLY with master.dbo.spt_values table to get list of numbers and generate dates:
select ID,T.number+1 as YEAR,
--generate date_start using T.number
dateadd(year,T.number,START_DATE)date_start,
--generate end_date: adding 1 year to start date
dateadd(dd,-1,dateadd(year,1,dateadd(year,T.number,START_DATE)))date_end
from Table
cross apply
master.dbo.spt_values T
where T.type='P' and T.number<YEARS