检查日期是否介于其他表的两个日期之间

Question

I have two tables as follow:

subscriptions:

user_id
started_at
ended_at

The subscription table contains historical membership for all the users. Users who never had subscriptions will not be included in this table. A user with X historical subscriptions will have X records in the table. For a user's most recent subscription, the col ended_at will be null if the membership is currently active.

transactions:

transaction_id (PK)
user_id
started_at
amount

This table tracks, for each historical transaction, the initiation time as well as amount along with user_id.

How can we know if the corresponding user has active gold membership at the time of making the transaction?

The output should look like something like.

transaction_id
user_membership_active (bool)

How can we check if a date from table1 lies between two dates from another table? Any help is appreciated.

Answer 1

Are you expecting something like this?

SELECT transaction_id,
       CASE
         WHEN ended_at IS NULL THEN 'True'
         ELSE 'False'
       END user_membership_active
FROM   transactions t1
       INNER JOIN subscriptions t2
               ON t1.user_id = t2.user_id
                  AND t1.started_at BETWEEN t2.started_at AND
                                            ISNULL(t2.ended_at, GETDATE())

Answer 2

Based on what you want to display, I'm assuming you would still insert a record in transactions table, regardless of whether there exists an active membership or not.

If you want to do this check after transaction record is inserted -

Select t.transaction_id,
case when t.started_at >= s.started_at 
and t.started_at < NVL(s.ended_at, SYSDATE())
then 'Y'  -- using Y/N for your boolean output
else 'N'
end as user_membership_active
from transactions t 
inner join subscriptions s on t.user_id = s.user_id

Answer 3

If I understand correctly, you just want a flag. One method uses exists :

select t.*
       (exists (select 1
                from subscriptions s
                where s.user_id = t.user_id and
                      s.started_at <= t.started_at and
                      (s.ended_at > t.started_at or s.ended_at is null
                      )
               )
       ) as user_membership_active
from transactions t;

For performance, you want an index on subscriptions(user_id, started_at, ended_at) .

Note: If a person has multiple concurrent subscriptions, this does not multiply the number of rows in the result set.