SQL Query Preference Ordering

Data and Databases
1

For SQL, if DeliveryLog contains both ‘processing’ and another state per email, only the non-processing state is returned. Sample data:

|UserEmail      | State      |
|---------------|------------|
|user1@mail.com | confirmed  |
|user2@mail.com | confirmed  |
|user3@mail.com | failed     |
|user4@mail.com | processing |
2

In addressing such queries, I have found that using subqueries to filter out processing states within a reusable common table expression can lead to more manageable SQL code. It helps avoid ambiguity when multiple states are present for an email. In my experience, carefully testing the query on sample datasets and ensuring proper indexing have been critical to maintain performance while accurately capturing the intended state. This method provides clear logic, reducing errors in state resolution and scaling effectively with increased data volumes.

3

hey, i like this method! i wonder how you handle cases with multiple non-procssing states - do you pick the latest? what aproach did u try for scalability in larger datasets? keen to learn more!