T-SQL - Next row with greater value, continuously - sql-server

Question

I have table described bellow from which I need to select all rows with [Value] greater for example at least 5 points than [Value] from previous row (ordered by [Id]). Starting with first row of [Id] 1, desired output would be:
[Id] [Value]
---------------
1 1
4 12
8 21
Code:
declare #Data table
(
[Id] int not null identity(1, 1) primary key,
[Value] int not null
);
insert into #Data ([Value])
select 1 [Value]
union all
select 5
union all
select 3
union all
select 12
union all
select 8
union all
select 9
union all
select 16
union all
select 21;
select [t1].*
from #Data [t1];
Edit:
So, based on JNevill's and Hogan's answers I end with this:
;with [cte1]
as (
select [t1].[Id],
[t1].[Value],
cast(1 as int) [rank]
from #Data [t1]
where [t1].[Id] = 1
union all
select [t2].[Id],
[t2].[Value],
cast(row_number() over (order by [t2].id) as int) [rank]
FROM [cte1] [t1]
inner join #Data [t2] on [t2].[value] - [t1].[value] > 5
and [t2].[Id] > [t1].[Id]
where [t1].[rank] = 1
)
select [t1].[Id],
[t1].[Value]
from [cte1] [t1]
where [t1].[rank] = 1;
which is working. Alan Burstein answer is correct too (but applicable only on MSSQL 2012+ - due to LAG fc). I will do some performance tests (I'm on 2016 version) and will see performance over my real data (approx. 30 millions of records).

Answer 1

If you are on 2012+ you can use LAG which will provide a better performing solution that a recursive CTE. I'm including your sample data so you can just copy/paste/test...
-- Your sample data
DECLARE #Data TABLE
(
Id int not null identity(1, 1) primary key,
Value int not null
);
insert into #Data ([Value])
select 1 [Value] union all select 5 union all select 3 union all select 12 union all
select 8 union all select 9 union all select 16 union all select 21;
-- Solution using window functions
WITH
prevRows AS
(
SELECT t1.Id, t1.Value, prevDiff = LAG(t1.Value, 1) OVER (ORDER BY t1.id) - t1.Value
FROM #Data t1
),
NewPrev AS
(
SELECT t1.Id, t1.Value, NewDiff = Value - LAG(t1.Value,1) OVER (ORDER BY t1.id)
FROM prevRows t1
WHERE prevDiff <= -5 OR prevDiff IS NULL
)
SELECT t1.Id, t1.Value
FROM NewPrev t1
WHERE NewDiff >= 5 OR NewDiff IS NULL;

Answer 2

I believe the best way to pull this off is using a recursive CTE. A Recursive CTE is a special type of CTE that refers back to itself. It's made up of two parts.
The recursive seed/anchor which establishes the beginning of the recursion. In your case, record with ID=1.
The recursive term/member which is the statement that refers back to itself by the name of the CTE. Here we pull through the next record that is greater than 5 from the previous found record according to the ID sorted ascending.
Code:
WITH RECURSIVE recCTE AS
(
/*Select first record for recursive seed/anchor*/
SELECT
id,
value,
cast(1 as INT) as [rank]
FROM table
WHERE id = 1
UNION ALL
/*find the next value that is more than 5 from the current value*/
SELECT
table.id,
table.value
ROW_NUMBER() OVER (ORDER BY id)
FROM
recCTE INNER JOIN table
ON table.value - recCTE.value > 5
AND table.id > recCTE.id
WHERE recCTE.[rank]=1
)
SELECT id, value FROM recCTE;
I've made use of the Row_Number() Window Function to find the rank of the matching record by ID sorted Ascending. With the WHERE clause in the recursive term we only grab the first found record that is 5 more than the previous found record. Then we head into the next recursive step.

Answer 3

You can do it with a recursive CTE
with find_values as
(
-- Find first value
SELECT Value
FROM #Table
ORDER BY ID ASC
FETCH FIRST 1 ROW ONLY
UNION ALL
-- Find next value
SELECT Value
FROM #Table
CROSS JOIN find_values
WHERE Value >= find_values.Value + 5
ORDER BY ID ASC
FETCH FIRST 1 ROW ONLY
)
SELECT *
FROM find_values