The correct answer is an inner join between the fact table and the dimension tables. In a star schema, the fact table contains foreign keys that link to dimension tables, and an inner join ensures that only rows with matching keys in both tables are returned, which is essential for accurate aggregation. This query requires joining sales_fact with product_dim to map product keys to categories and with time_dim to filter for the last month, and an inner join naturally excludes any orphaned records that would skew total sales. On the CompTIA Data+ DA0-001 exam, this tests your understanding of star schema query patterns and the role of referential integrity; a common trap is assuming a left join is needed, but in a well-designed warehouse, all fact rows should have corresponding dimension entries, making inner join the standard. Remember the memory tip: “Inner joins keep the star clean—no missing dimensions, no missing data.”
DA0-001 Comparing and Contrasting Data Concepts Practice Question
This DA0-001 practice question tests your understanding of comparing and contrasting data concepts. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
An e-commerce company uses a star schema for its data warehouse. The fact table 'sales_fact' contains foreign keys to dimension tables: customer_dim, product_dim, time_dim, and store_dim. A business user wants to know the total sales for each product category in the last month. Which join operation is required to retrieve this data?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Inner join between fact table and dimension tables
To retrieve total sales for each product category, you need to join the fact table with the product dimension table to map product keys to categories, and with the time dimension table to filter on the last month. An inner join is correct because it returns only rows where matching keys exist in both tables, which is the standard approach for star-schema queries where all required dimension attributes are present. This ensures that only valid sales transactions with corresponding product and time entries are included in the aggregation.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Self-join on the fact table
Why it's wrong here
Self-join is used for hierarchical data within the same table.
✗
Cross join between fact and dimension tables
Why it's wrong here
Cross join combines all rows, leading to incorrect aggregation.
✓
Inner join between fact table and dimension tables
Why this is correct
Inner join returns only matching rows, which is typical in star schema queries.
Related concept
Read the scenario before looking for a memorised answer.
✗
Left outer join between fact and dimension tables
Why it's wrong here
Outer join may include nulls, but facts should have matching dimensions.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the need for a left outer join to 'preserve all fact rows,' but in a well-designed star schema with referential integrity, inner join is sufficient and more performant, and left outer join is only needed when fact rows might lack matching dimension keys (e.g., orphaned records).
Detailed technical explanation
How to think about this question
In a star schema, foreign keys in the fact table are assumed to have referential integrity with dimension tables, so an inner join is both efficient and semantically correct. Under the hood, the database optimizer can use index nested loop joins or hash joins on the foreign key columns, minimizing I/O. A real-world scenario where this matters is when dimension tables contain slowly changing dimensions (SCD); an inner join ensures that only current or relevant dimension attributes are used, avoiding duplication from historical records.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the DA0-001 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Comparing and Contrasting Data Concepts — This question tests Comparing and Contrasting Data Concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Inner join between fact table and dimension tables — To retrieve total sales for each product category, you need to join the fact table with the product dimension table to map product keys to categories, and with the time dimension table to filter on the last month. An inner join is correct because it returns only rows where matching keys exist in both tables, which is the standard approach for star-schema queries where all required dimension attributes are present. This ensures that only valid sales transactions with corresponding product and time entries are included in the aggregation.
What should I do if I get this DA0-001 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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