PL-300 Question 6

Community Discussion

Written by other learners. Comments can disagree with the marked answer — check the official documentation when in doubt.

• 1

  Answer (merge order & join kinds): ProductSubCategory → ProductCategory: Left Outer (keep all subcategories; bring category when present) Product → (ProductSubCategory+Category result): Inner (every product has a subcategory; only matched rows needed).

• 2

  For question 1: Both Left Join and Inner Join would return the same result here because every Product has a matching ProductSubCategory. However, Microsoft’s best practice in Power Query is to use Left Join when you want to ensure that all rows from the left table are preserved. For question 2: Use Left Join. Since not every ProductSubCategory has a ProductCategory, a Left Join keeps all SubCategories and simply returns blank values for the missing Categories instead of dropping rows.

• 3

  1. Never make assumptions when solving these questions. The statement 'Every Product has a ProductSubCategory' does not imply that 'Every ProductSubCategory also has a Product.' Therefore, an inner join is correct. A left outer join would only be appropriate if the question mentioned the possibility of missing values. Always stick strictly to what is asked, without adding your own scenarios. 2. We are only told that not every ProductSubCategory has a parent ProductCategory. This does not imply that not every ProductCategory has a child ProductSubCategory. Therefore, it is possible for a product to either have or not have a subcategory. In this situation, using a Left Outer Join is more appropriate, as it ensures that all subcategories are retained while only bringing in the matching product categories.