Question

I have a table without identity field. the structure about:

Date date,
SomeFK int,
Key float,
Value float

I need to be able to select not using cursor something like

select Key, PrevKey, Value from ... where Key > @a and Key <= @b

where the PrevKey has to be a Key from previous record, given that the recordset ordered by Key

If data like this:

0.1, 2.0
0.2, 3.0
0.3, 5.0
0.4, 4.0

Then expected result for @a=0.15 and @b=0.3

0.2, 0.1, 3.0
0.3, 0.2, 5.0

What I am trying to do is to calculate a formula: SUM(Value[i] * (Key[i] – Key[i-1]))

Answer 1

One way you could try is this CTE approach:

DECLARE @Data TABLE ([Key] FLOAT PRIMARY KEY, Value FLOAT)
INSERT @Data VALUES(0.1, 2.0),(0.2, 3.0), (0.3, 5.0), (0.4,4.0)

;WITH CTEData AS
(
SELECT ROW_NUMBER() OVER(ORDER BY [Key]) AS RowNo,
    [Key], Value
FROM @Data
)

SELECT d1.[Key], d2.[Key] AS PreviousKey, d1.Value
FROM CTEData d1
    INNER JOIN CTEData d2 ON d1.RowNo-1 = d2.RowNo

Edit
Just seen that your PK is not exclusively on “Key”, which the above example assumes.