Multiple conditions (A and B) and not (C and D). How should the SQL query look like?

Question

Let's say we have a e-shop and all users' events in a single table. The events table looks like this:

id user_id type             time             comment
1  1       visit_site       2022-04-07 14:08
1  1       add_item_to_cart 2022-04-07 14:17
1  1       add_item_to_cart 2022-04-07 14:17
1  1       checkout         2022-04-07 14:22
1  1       pay              2022-04-07 14:25
1  2       visit_site       2022-04-07 14:30
1  2       add_item_to_cart 2022-04-07 14:40
1  2       add_item_to_cart 2022-04-07 14:44
1  2       checkout         2022-04-07 14:47
1  2       pay              2022-04-07 14:50

So there are multiple event types, they have timestamp (when it happened) and user that is the actor.

Let's say I want to find all users that did add items to cart and did buy on the next day. I would assume the SQL query should be

SELECT DISTINCT
  user_id
FROM
  user_event
WHERE
  (type = 'add_item_to_cart' AND time BETWEEEN '2022-04-07 00:00' AND '2022-04-08 00:00') AND
  (type = 'buy' AND time BETWEEEN '2022-04-08 00:00' AND '2022-04-09 00:00')

Now, I understand that the above condition is basically equal to:

WHERE
  type = 'add_item_to_cart' AND time BETWEEEN '2022-04-07 00:00' AND '2022-04-08 00:00' AND
  type = 'buy' AND time BETWEEEN '2022-04-08 00:00' AND '2022-04-09 00:00'

which will return always empty results because we apply two conditions to column time with date ranges that don't intersect.

So I have 3 questions

1. How do I rewrite the query so that I get customers that added item to cart in 1 date range and bought in another date range ?
2. The above condition actually would match purchases made almost 2 days from adding to cart, i.e. '2022-04-07 00:01' - added to cart, '2022-04-08 23:58' - bought. How do I make a condition related to previous one, i.e. match buys strictly less than 1 day from last date of checkout (with matching user id) ?
3. Is there a way to force that events are related to the same user, so that query doesn't return user who bought item <1 day after someone else (with different user_id) added an item to cart ?

Answer 1

Instead of using a WHERE statement within the same SELECT, you can try applying a SELF JOIN on the transactions made by the same users on a difference of one day:

SELECT DISTINCT
    t1.id,
    t1.user_id,
    t1.time AS time1,
    t1.type AS type1,
    t2.time AS time2,
    t2.type AS type2
FROM 
    user_event t1 
INNER JOIN 
    user_event t2
ON 
    t1.user_id = t2.user_id
AND 
    DATEDIFF(t2.time, t1.time) = 0
WHERE 
    t1.type = 'add_item_to_cart'
AND 
    t2.type = 'pay'

This solution answers to all your questions. You can find a fiddle here: https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=3066b711f72ce7444859be1a824d9eb3. The input rows of this fiddle contain three kinds of users:

1. user who bought the same day,
2. user who bought the day after (targeted user),
3. user who bought two days after.