Find purchase if same item on different days - sql

Question

I'm trying to find customers that bought the same item more than once in different days. I got it partially working. I can't get the customer first/last name and item_name without adding it to the group by clause. In addition, I want to include a count if how many times the same uten was purchased on different days.
I suspect that group by is probably not the best solution. Would this be better solved using a self JOIN or perhaps a lead?
CREATE TABLE customers
(CUSTOMER_ID, FIRST_NAME, LAST_NAME) AS
SELECT 1, 'Abby', 'Katz' FROM DUAL UNION ALL
SELECT 2, 'Lisa', 'Saladino' FROM DUAL UNION ALL
SELECT 3, 'Jerry', 'Torchiano' FROM DUAL;
CREATE TABLE items
(PRODUCT_ID, PRODUCT_NAME) AS
SELECT 100, 'Black Shoes' FROM DUAL UNION ALL
SELECT 101, 'Brown Shoes' FROM DUAL UNION ALL
SELECT 102, 'White Shoes' FROM DUAL;
CREATE TABLE purchases
(CUSTOMER_ID, PRODUCT_ID, QUANTITY, PURCHASE_DATE) AS
SELECT 1, 100, 1, TIMESTAMP'2022-10-11 09:54:48' FROM DUAL UNION ALL
SELECT 1, 100, 1, TIMESTAMP '2022-10-11 19:04:18' FROM DUAL UNION ALL
SELECT 2, 101,1, TIMESTAMP '2022-10-11 09:54:48' FROM DUAL UNION ALL
SELECT 2,101,1, TIMESTAMP '2022-10-17 19:04:18' FROM DUAL UNION ALL
SELECT 3, 101,1, TIMESTAMP '2022-10-11 09:54:48' FROM DUAL UNION ALL
SELECT 3,102,1, TIMESTAMP '2022-10-17 19:04:18' FROM DUAL;
With CTE as (
SELECT customer_id
,product_id
,trunc(purchase_date)
FROM purchases
GROUP BY customer_id
,product_id
,trunc(purchase_date)
)
SELECT customer_id, product_id
FROM CTE
GROUP BY customer_id ,product_id
HAVING COUNT(1)>1

Answer 1

I would use exists logic here:
SELECT DISTINCT c.first_name, c.last_name
FROM customers c
INNER JOIN purchases p
ON p.customer_id = c.customer_id
WHERE EXISTS (
SELECT 1
FROM purchases p2
WHERE p2.customer_id = p.customer_id AND
p2.product_id = p.product_id AND
TRUNC(p2.purchase_date) <> TRUNC(p.purchase_date)
);
In plain English, the above query says to find all customers who bought the same product but on different dates.

Answer 2

This might be one option: use count function in its analytic form and the fetch rows where that count is larger than 1; according to data you posted, it is Lisa who bought brown shoes on two different dates.
SQL> WITH
2 temp
3 AS
4 ( SELECT c.first_name,
5 i.product_name,
6 TRUNC (p.purchase_date),
7 COUNT (*) OVER (PARTITION BY c.first_name, i.product_name) cnt
8 FROM purchases p
9 JOIN customers c ON c.customer_id = p.customer_id
10 JOIN items i ON i.product_id = p.product_id
11 GROUP BY c.first_name, i.product_name, TRUNC (p.purchase_date))
12 SELECT DISTINCT first_name, product_name, cnt
13 FROM temp
14 WHERE cnt > 1;
FIRST PRODUCT_NAM CNT
----- ----------- ----------
Lisa Brown Shoes 2
SQL>