SQL Server query to extract all rows - sql

Question

I've two database tables, one called "Headers" and one called "Rows".
The structure is:
Header: IDPK | Description
Row: IDPK | IDPK_Header | Item_ID | Qty
I need to do a query that says: "From a Header, IDPK find another header that have the same number of rows and the same item ID and quantity".
For example:
Header Rows
IDPK Description IDPK Item_ID Qty
1 'Test1' 1 'A' 10
1 'Test1' 2 'B' 20
2 'Test2' 3 'A' 10
2 'Test2' 4 'B' 20
3 'Test3' 5 'A' 5
3 'Test3' 6 'B' 20
4 'Test4' 7 'A' 10
Header Test1 match Test2 but not Test3 and Test4
The problem is that the number of rows must be exactly the same. I try with ALL operator but without luck.
How I can do the query with an eye for the performance? The two tables can be very huge (~500.000 records).

Answer 1

Assuming there are no duplicates:
with r as (
select r.*, count(*) over (partition by idpk_header) as num_items
from rows r
)
select r1.idpk_header, r2.idpk_header
from r r1 join
r r2
on r1.item_id = r1.item_id and r2.qty = r1.qty and r2.num_items = r1.num_items
group by r1.idpk_header, r2.idpk_header, r1.num_items
having count(*) = r1.num_items;
Basically, this does a self-join on the items, so you only get matches. The on validates that the two have the same number of items. And the having guarantees that all match.
Note: This version returns each match of the header to itself. That is a nice check. You can of course filter this out in the on or a where clause.
If you do have duplicate items, you can simply replace r with:
select idpk_header, item_id, sum(qty) as qty,
count(*) over (partition by idpk_header) as num_items
from rows r
group by idpk_header, item_id;

Answer 2

I woul suggest using a forxml query in order to create the list of items per IDPK. Next I would search for matching item lists and quantities. See following example:
DECLARE #Headers TABLE(
IDPK INT,
Description NVARCHAR(100)
)
DECLARE #Rows TABLE(
IDPK INT,
ITEMID NVARCHAR(1),
Qty INT
)
INSERT INTO #Headers VALUES
(1, 'Test1'),
(2, 'Test2'),
(3, 'Test3'),
(4, 'Test4'),
(5, 'Test5')
INSERT INTO #Rows VALUES
(1, 'A', 10),
(1, 'B', 20),
(2, 'A', 10),
(2, 'B', 20),
(3, 'A', 5 ),
(3, 'B', 20),
(4, 'C', 10),
(5, 'A', 10),
(5, 'C', 20)
;
WITH cteHeaderRows AS(
SELECT IDPK
,ItemIDs=STUFF(
(
SELECT ',' + CAST(ITEMID AS VARCHAR(MAX))
FROM #Rows t2
WHERE t2.IDPK = t1.IDPK
ORDER BY ITEMID, QTY
FOR XML PATH('')
),1,1,''
)
,Qtys=STUFF(
(
SELECT ',' + CAST(Qty AS VARCHAR(MAX))
FROM #Rows t2
WHERE t2.IDPK = t1.IDPK
ORDER BY ITEMID, QTY
FOR XML PATH('')
),1,1,''
)
FROM #Rows t1
GROUP BY IDPK
),
cteFilter AS(
SELECT h1.IDPK AS IDPK1, h2.IDPK AS IDPK2
FROM cteHeaderRows h1
JOIN cteHeaderRows h2 ON h1.IDPK != h2.IDPK AND h1.ItemIDs = h2.ItemIDs AND h2.Qtys = h1.Qtys
)
SELECT DISTINCT h.IDPK, h.Description, r.ItemID, r.Qty
FROM #Headers h
JOIN cteFilter f ON f.IDPK1 = h.IDPK
JOIN #Rows r ON r.IDPK = f.IDPK1
ORDER BY 1,3,4