How to bring the last 5 register of each ID with SQL? - sql-server

Question

I have a table with the purchase registers. There are all the purchase registers of a Pet Shop, since 2010.
I need some help to bring only the last five purchase of each client.
I was trying, but it is not working. It brings me the last 5 registers of all the table, and not of each client.
SELECT TOP (5) [client_name],
[purchase_date],
[item]
FROM [Pet_Shop]
ORDER BY client_name
WHERE client_name in ('John', 'Mary', 'Austin')
I need this kind of return:
client_name | purchase_date | item
___________________________________
John | 2019-09-14 | food
John | 2019-09-13 | ball
John | 2019-09-12 | shampoo
John | 2019-09-11 | cookie
John | 2019-09-11 | food
Mary | 2019-09-14 | collar
Mary | 2019-07-14 | food
Mary | 2019-06-14 | toy
Mary | 2019-06-14 | hamster
Mary | 2019-05-14 | food
Austin | 2019-09-18 | food
Austin | 2019-09-11 | collar
Austin | 2019-09-10 | toy
Austin | 2019-09-09 | catnip
Austin | 2019-09-11 | food

Answer 1

Use ROW_NUMBER():
SELECT *
FROM (
SELECT
client_name,
purchase_date,
item,
ROW_NUMBER() OVER(PARTITION BY client_name ORDER BY purchase_date desc) rn
FROM Pet_Shop
WHERE client_name in ('John', 'Mary', 'Austin')
) x
WHERE rn <= 5
ORDER BY client_name

Answer 2

You can use CROSS APPLY like this:
DECLARE #Registry TABLE (client_name VARCHAR(100), purchase_date DATETIME, item INT)
INSERT INTO #Registry
(client_name, purchase_date, item)
VALUES
('Client1', '1/1/2019', 1),
('Client1', '2/1/2019', 2),
('Client1', '3/1/2019', 3),
('Client1', '4/1/2019', 4),
('Client1', '5/1/2019', 5),
('Client1', '6/1/2019', 6),
('Client1', '7/1/2019', 7),
('Client2', '1/1/2019', 1),
('Client2', '2/1/2019', 2),
('Client2', '3/1/2019', 3),
('Client2', '4/1/2019', 4),
('Client2', '5/1/2019', 5),
('Client2', '6/1/2019', 6),
('Client2', '7/1/2019', 7)
;WITH Clients AS (
SELECT client_name FROM #Registry GROUP BY client_name
)
SELECT C.*, P.purchase_date, P.item
FROM Clients AS C
CROSS APPLY
(
SELECT TOP 5 R.purchase_date, R.item
FROM #Registry R
WHERE R.client_name = C.client_name
ORDER BY R.purchase_date DESC
) P
ORDER BY C.client_name, P.purchase_date, P.item
Here is the result:
client_name purchase_date item
Client1 2019-03-01 00:00:00.000 3
Client1 2019-04-01 00:00:00.000 4
Client1 2019-05-01 00:00:00.000 5
Client1 2019-06-01 00:00:00.000 6
Client1 2019-07-01 00:00:00.000 7
Client2 2019-03-01 00:00:00.000 3
Client2 2019-04-01 00:00:00.000 4
Client2 2019-05-01 00:00:00.000 5
Client2 2019-06-01 00:00:00.000 6
Client2 2019-07-01 00:00:00.000 7