Top 3 Grain Interview Questions
Browse 3 real-world technical and behavioral interview questions about Grain. Review scenarios, edge cases, and architectural best practices.
A customer moves from London to Manchester. Last quarter's regional sales report now shows different numbers. Why, and how do you stop it?
The dimension was overwritten, so historical facts joined to it now report the customer's current region rather than the region they were in when they bought. Keeping history means versioning the dimension row and joining facts to the version that was current at the time, not to the customer.
In a modern columnar warehouse, would you still build a star schema or just use one wide table?
Settle the grain first - what one fact row means. A star still earns its place for conformed dimensions and type-2 history, while a wide table is a serving artefact for one known pattern. A warehouse differs from a lake by having a modelled contract, not by where the bytes live.
Two dashboards report different revenue for the same month. How do you find out why, and how do you stop it happening again?
Reconcile the two numbers row by row before touching the pipelines: the cause is almost always a grain mismatch that fans out a join, a filter difference over refunds or test accounts, or two timestamps meaning different things. The fix is one certified definition that both dashboards are forced to call.