T-SQL to efficiently select the most recent previous order item - sql-server

Question

I am trying to figure out an efficient way to select the previous order item for each order item in a current order.
For example each order has a set of order items, i.e. the amount of an article/product that was ordered. For a particular customer, this would result in an order history as illustrated below:
I would like to find the "previous" orderitem for each orderitem in a particular order, i.e. the most recent orderitem for the same customer and article product preceding the order in question. These are highlighted above. Note that the previous orderitem may not be from the previous order of that customer.
Selecting it for a particular orderitem in an order with :datetime for :customerID and :articleID could be done like this:
select top(1) *
from orderitem
join order on order.orderid = orderitem.orderid
where order.customerID = :customerID
and order.datetime < :datetime
and orderitem.articleID = :articleID
order by order.datetime desc
However, is there an efficient way rather than looping or using a sub-select to select all previous orderitems for a given order with a single select or some type of join?

Answer 1

Your description of your desired outcome isn't quite clear. This sounds like you want a pivot table for the customer with the most recent order on the left. Here's an example of using PIVOT to accomplish the desired output. It only has order dates, if you want order numbers, that can be added in the column names.
--Create tables for test data.
CREATE TABLE order_hdr (
order_number int
, order_date date
, customer_id int
);
CREATE TABLE order_lines (
order_number int
, line_number int
, quantity int
, item_id nvarchar(50)
);
--Populate test data.
INSERT INTO order_hdr (order_number, order_date, customer_id)
VALUES (111, '1/1/2022', 12345)
, (112, '1/2/2022', 45678)
, (113, '1/2/2022', 87964)
, (114, '1/3/2022', 12345)
, (115, '1/3/2022', 45678)
, (116, '1/3/2022', 87964)
, (117, '1/9/2022', 12345)
, (118, '1/9/2022', 45678)
, (119, '1/9/2022', 87964)
;
INSERT INTO order_lines (order_number, line_number, quantity, item_id)
VALUES (111, 1, 4, 'Article A')
, (111, 2, 2, 'Article B')
, (111, 3, 3, 'Article C')
, (111, 4, 1, 'Article D')
, (112, 1, 1, 'Article B')
, (112, 2, 1, 'Article C')
, (112, 3, 1, 'Article D')
, (113, 1, 11, 'Article B')
, (113, 2, 9, 'Article C')
, (113, 3, 8, 'Article D')
, (114, 1, 4, 'Article C')
, (114, 2, 6, 'Article D')
, (115, 1, 77, 'Article A')
, (115, 2, 22, 'Article B')
;
--Variables for filtering data.
DECLARE #CustID int = 12345;
DECLARE #ReportDate date = '2/1/2022';
DECLARE #ItemID nvarchar(50) = 'Article A'; --Not used.
--Create a variable to hold the string of dates.
DECLARE #dates nvarchar(max);
--Get last 5 distinct order dates.
SET #dates = STUFF((
SELECT ',"' + CAST(order_date as nvarchar) + '"'
FROM (
SELECT DISTINCT TOP (5) order_date
FROM order_hdr
WHERE customer_id = #CustID
ORDER BY order_date DESC
) as prelim
FOR XML PATH('')
),1,1,'');
--For debugging, show the string of dates.
PRINT 'Date string contents: ' + #dates;
--For debugging/testing, here is a static query using PIVOT
PRINT 'Test Query using Static Order Dates:';
SELECT item_id, "1/3/2022", "1/2/2022"
FROM (
SELECT
oh.order_date
, ol.item_id
, ol.quantity
FROM order_hdr as oh
INNER JOIN order_lines as ol
ON ol.order_number = oh.order_number
WHERE oh.customer_id = #CustID
) as st
PIVOT
(
SUM(quantity)
FOR order_date IN ("1/3/2022", "1/2/2022")
) as pt
;
--Now create a text variable to hold the dynamic SQL. We will substitue the place holders for the order dates or order numbers.
DECLARE #sqlText nvarchar(max) = N'
SELECT item_id, {{0}}
FROM (
SELECT
oh.order_date
, ol.item_id
, ol.quantity
FROM order_hdr as oh
INNER JOIN order_lines as ol
ON ol.order_number = oh.order_number
WHERE oh.customer_id = {{1}}
) as st
PIVOT
(
SUM(quantity)
FOR order_date IN ({{0}})
) as pt
;
';
--Replace the placeholders with the date string;
SET #sqlText = REPLACE(#sqlText, '{{0}}', #dates);
--Replace the placeholders with the date string;
SET #sqlText = REPLACE(#sqlText, '{{1}}', CAST(#CustID as nvarchar));
--Show query for debugging.
PRINT 'The dynamic query: ' + CHAR(13) + #sqlText;
--Execute the dynamic sql.
PRINT 'Final Query using Dynamic Order Dates:';
EXEC (#sqlText);
Test Query using Static Order Dates:
item_id
1/3/2022
1/2/2022
Article A
null
null
Article B
null
null
Article C
4
null
Article D
6
null
Date string contents: "2022-01-09","2022-01-03","2022-01-01"
The dynamic query:
SELECT item_id, "2022-01-09","2022-01-03","2022-01-01"
FROM (
SELECT
oh.order_date
, ol.item_id
, ol.quantity
FROM order_hdr as oh
INNER JOIN order_lines as ol
ON ol.order_number = oh.order_number
WHERE oh.customer_id = 12345
) as st
PIVOT
(
SUM(quantity)
FOR order_date IN ("2022-01-09","2022-01-03","2022-01-01")
) as pt
;
Final Query using Dynamic Order Dates:
item_id
2022-01-09
2022-01-03
2022-01-01
Article A
null
null
4
Article B
null
null
2
Article C
null
4
3
Article D
null
6
1
fiddle