Looking at user’s first/last transaction details is a common requirement. So given that you have a “user_transaction_details” table which looks something like:
Transaction_id | user_id | transaction_date | purchase amount
How would get first/last transaction details for each user account?
Here’s a design pattern:
select AllTransactions.user_id,AllTransactions.purchase_amt from user_transaction_details AllTransactions inner join ( select user_id, min(transaction_timestamp) as first_transaction_timestamp from user_transaction_details group by user_id ) FirstTransaction on AllTransactions.user_id = FirstTransaction.user_id and AllTransactions.transaction_timestamp = FirstTransaction.first_transaction_timestamp
To get the last transaction details for each user account, replace min function with max and that should be it.
Note: Depending on your data model and how you used it in the join, it might be that there would be multiple rows marked as “first/last” transaction and so would want to spend some time figuring out how to deal with these multiple row situation especially if you’re planning to further join this data.
In this post, I shared a design pattern to write a SQL query to get first/last transaction details for each user account type.
Question for you:
How would you solve this problem? Share you query in the comments section!