Group SQL data and split into columns - mysql

Question

I have a table with the following columns, where the timestamp column indicates the date the user viewed a product, and the purchase column if the view generated a purchase:
id
userId
productId
timestamp
purchase
1
2
4
2022-01-07
0
2
2
4
2022-01-10
1
3
2
4
2022-01-12
0
4
2
4
2022-01-16
1
How to group the data by userId and productId in order to return as follows:
id
userId
productId
firstView
lastView
firstPurchase
1
2
4
2022-01-07
2022-01-16
2022-01-10
For the firstView and listView columns I know I should use Min() and Max(), but the firstPurchase column I can't display. I tried using CASE when column purchase = 1 but it didn't work.

Answer 1

You need to use MIN(CASE WHEN purchase = 1 THEN "timestamp" ELSE NULL END), like this:
create table your_table (id int, userId int, productId int, "timestamp" date, purchase int)
insert into your_table (id, userId, productId, "timestamp", purchase)
values
(1,2,4,'2022-01-07 00:00:00',0),
(2,2,4,'2022-01-10 00:00:00',1),
(3,2,4,'2022-01-12 00:00:00',0),
(4,2,4,'2022-01-16 00:00:00',1);
SELECT
userId,
productId,
MIN(timestamp) AS firstView,
MAX(timestamp) AS lastView,
MIN(CASE WHEN purchase = 1 THEN "timestamp" ELSE NULL END) AS firstPurchase
FROM your_table
GROUP BY
userId,
productId;
p.s. please don't call a column "timestamp" :)

Answer 2

Try this:
SELECT t1.id, t1.userId, t1.productId, t1.timestamp,
(SELECT t3.timestamp
FROM yourtable t3
WHERE t3.userId = t1.userId
AND t3.productId = t1.productId
AND NOT EXISTS
(SELECT 1
FROM yourtable t4
WHERE t4.userId = t3.userId
AND t4.productId = t3.productId
AND t4.timestamp > t3.timestamp
)
) as lastView,
(SELECT t3.timestamp
FROM yourtable t3
WHERE t3.userId = t1.userId
AND t3.productId = t1.productId
AND t3.purchase = 1
AND NOT EXISTS
(SELECT 1
FROM yourtable t4
WHERE t4.userId = t3.userId
AND t4.productId = t3.productId
AND t4.timestamp < t3.timestamp
AND t4.purchase = 1
)
) as firstPurchase
FROM yourtable t1
WHERE NOT EXISTS
(SELECT 1 FROM yourtable t2
WHERE t1.userId = t2.userId
AND t1.productId = t2.productId
AND t2.timestamp < t1.timestamp)
See Sql Fiddle