フリー問題

問題文

Before adding a lookup join, an architect wants to guarantee the result keeps exactly one row per left record. What must be true of the join to ensure that grain is preserved?

選択肢

1. As long as the left side of the join is unique, and has one row per record, the grain is preserved regardless of the lookup side in the recipe.
2. The security predicate guarantees one row per left record.
3. The lookup side must be unique at the join key so that every left record has at most one match and the grain stays one row per left record.
4. Choosing an inner join instead of a left join preserves the one-row-per-left grain.