Write a query for the top 5 product pairs bought together by the same user in the same transaction.
The Databricks Data Engineer self-join classic. One inequality predicate does all the work, get it wrong and you double-count every pair and match products with themselves. Here's the clean version and the fan-out trap.
Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.
The Databricks Data Engineer self-join classic. One inequality predicate does all the work, get it wrong and you double-count every pair and match products with themselves. Here's the clean version and the fan-out trap.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.
