How to get records that between m records back and n records forward from a reference row - Non-sequential data - sql

Question

My scenario is as follows:
I have a reference record, say, ProductId = 1
The records each have a non-unique ItemTypeId
I would like to fetch records that exists between the following points
START POINT being 2 records BACKWARDS of type ItemTypeId = 1, from record of ProductId =1
END POINT being 3 records FORWARDS of type ItemTypeId = 1, from record of ProductId = 1
The query should get ALL data between the two points, inclusively
Here's a picture that illustrates this better than my words:
How would I structure my query to do this?
Any better way to do it without temp tables?
Thank-you!

Answer 1

Note that for this to work at all, you need that record ID to be an actual column in the table. Rows have no inherent order in a table.
With that in place, you can use LAG and LEAD to get what you want:
CREATE TABLE #t
(
RecordId INT IDENTITY(1,1),
ProductId INT,
ItemType INT
);
INSERT INTO #t(ProductId, ItemType)
VALUES
(5,1),(3,1),(7,3),(6,1),(2,7),
(1,1),(7,3),(8,1),(10,3),(9,5),
(11,1),(19,1),(17,4),(13,3);
WITH c1 AS
(
SELECT ProductId,
RecordId,
LAG(RecordId,2) OVER (ORDER BY RecordId) AS Back2,
LEAD(RecordId,3) OVER (ORDER BY RecordId) AS Forward3
FROM #t
WHERE ItemType = (SELECT ItemType FROM #t WHERE ProductId = 1)
),c2 AS
(
SELECT c1.Back2, c1.Forward3 FROM c1
WHERE c1.ProductId = 1
)
SELECT #t.*
FROM #t
INNER JOIN c2 ON #t.RecordId BETWEEN c2.Back2 AND c2.Forward3;

Answer 2

If you wanna do without using temp tables as you ask, the following solution work.
But it is not very nice i agree.
Well this is what i done :
CREATE DATABASE TEST;
USE TEST
CREATE TABLE PRODUCT
(
ProductId INT,
ItemType INT
)
INSERT INTO PRODUCT
VALUES
(5,1),
(3,1),
(7,3),
(6,1),
(2,7),
(1,1),
(7,3),
(8,1),
(10,3),
(9,5),
(11,1),
(19,1),
(17,4),
(13,3)
DECLARE product_cursor CURSOR FOR
SELECT * FROM PRODUCT;
OPEN product_cursor
DECLARE
#ProductId INT,
#ItemId INT,
#END_FETCH INT,
#countFrom INT,
#countTo INT
DECLARE #TableResult TABLE
(
RProductId INT,
RItemId INT
)
FETCH NEXT FROM product_cursor
INTO #ProductId, #ItemId
SET #END_FETCH = 0
SET #countFrom = 0
SET #countTo = 0
WHILE ##FETCH_STATUS = 0 AND #END_FETCH = 0
BEGIN
IF #ItemId = 1 AND (#countFrom = 0 AND #countTo = 0)
BEGIN
SET #countFrom = 3
SET #countTo = 3
END
ELSE
BEGIN
IF #countFrom > 0
BEGIN
--SELECT 'INSERTION : ' ,#ProductId,#ItemId
INSERT INTO #TableResult VALUES(#ProductId, #ItemId)
IF #ItemId = 1
BEGIN
SET #countFrom -= 1
--SELECT 'CountFrom : ', #countFrom
END
END
ELSE
BEGIN
IF #countTo > 0
BEGIN
--SELECT 'INSERTION : ' ,#ProductId,#ItemId
INSERT INTO #TableResult VALUES(#ProductId, #ItemId)
IF #ItemId = 1
BEGIN
SET #countTo -= 1
--SELECT 'CountTO : ', #countTo
END
END
ELSE
BEGIN
SET #END_FETCH = 1
END
END
END
FETCH NEXT FROM product_cursor
INTO #ProductId, #ItemId
END
CLOSE product_cursor
DEALLOCATE product_cursor
SELECT * FROM #TableResult
And this is the result i got :
RProductId RItemId
3 1
7 3
6 1
2 7
1 1
7 3
8 1
10 3
9 5
11 1
19 1
But i prefer the solution of #James Casey.
By the way, why won't you use temp table ?