In clustering design, which column is an excellent candidate to speed up joins in a large table with a join on PassportNo?

• A. City
• B. PassportNo
• C. Birth Year
• D. Current_Country

Answer: (B)

Clustering design aims to organize data so queries can prune non-relevant data quickly. When a large table is joined on PassportNo, clustering by PassportNo aligns the physical layout with the join predicate, letting the system prune micro-partitions that don’t contain the PassportNos in the join. This reduces the amount of data scanned and speeds up the join.

If you clustered on other columns like City, Birth Year, or Current_Country, those would only help queries that filter on those fields, not the join itself. They don’t narrow the data that needs to be scanned for the PassportNo predicate, so they’re less effective for speeding up this join.