- A
Store only the current value and rely on the fact table's timestamp to infer history
Why wrong: The fact table does not track dimension changes; this approach cannot reconstruct past states.
- B
Add effective start and end date columns for each dimension attribute
This standard SCD Type 2 pattern allows querying the state of the dimension at any point in time.
- C
Store only the current value in the dimension table and use an audit log for changes
Why wrong: An audit log is not directly joinable in BI queries without extra processing.
- D
Overwrite the old value with the new value
Why wrong: Overwriting erases historical data, violating the requirement for historical accuracy.
Question 926 of 1,000
Define data structures and implement SQL for Business Intelligence →mediumMultiple ChoiceObjective-mapped
Implementing Type 2 Slowly Changing Dimensions
This PCDE practice question tests your understanding of define data structures and implement sql for business intelligence. 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.
A company tracks customer demographics that change over time (e.g., address). They need to maintain historical accuracy in BI reports. Which approach correctly implements a Type 2 slowly changing dimension?
Quick Answer
The correct approach for implementing a Type 2 slowly changing dimension is to add effective start and end date columns for each dimension attribute. This method preserves full historical accuracy by recording when a given attribute value was valid, allowing BI queries to join fact tables based on a specific snapshot date and retrieve the correct historical context. On the Google Professional Cloud Database Engineer exam, this concept tests your understanding of temporal data modeling in BigQuery or Cloud SQL, often appearing in scenario-based questions about customer or product dimension tracking. A common trap is confusing Type 2 with Type 1 (overwrite) or Type 3 (alternate columns), but the key differentiator is the use of date ranges to track multiple versions over time. Remember the memory tip: “Start and end dates keep history straight; overwriting is a Type 1 mistake.”
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add effective start and end date columns for each dimension attribute
Option B is correct because Type 2 SCD requires preserving full history by adding effective start and end date columns to the dimension table. This allows BI reports to join on a fact row's transaction timestamp and retrieve the exact dimension attribute values that were current at that point in time, ensuring historical accuracy without data loss.
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.
- ✗
Store only the current value and rely on the fact table's timestamp to infer history
Why it's wrong here
The fact table does not track dimension changes; this approach cannot reconstruct past states.
- ✓
Add effective start and end date columns for each dimension attribute
Why this is correct
This standard SCD Type 2 pattern allows querying the state of the dimension at any point in time.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Store only the current value in the dimension table and use an audit log for changes
Why it's wrong here
An audit log is not directly joinable in BI queries without extra processing.
- ✗
Overwrite the old value with the new value
Why it's wrong here
Overwriting erases historical data, violating the requirement for historical accuracy.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Candidates often confuse Type 1 (overwrite) and Type 2 (versioning) SCDs, or mistakenly think an external audit log suffices for historical tracking. In Google PCDE, the key is that BI tools require directly joinable dimension versions with effective dates, not external logs, to accurately associate fact rows with historical attributes.
Detailed technical explanation
How to think about this question
In Type 2 SCD, each dimension row represents a version of the entity, with effective start and end dates (or a current flag) defining its validity period. When a fact row is loaded, its transaction date is used to join to the dimension row where the transaction date falls between the start and end dates, enabling point-in-time accuracy. A common subtlety is handling overlapping date ranges or future-dated changes, which requires careful ETL logic to close the previous version's end date and insert a new row with a start date equal to the change timestamp.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
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FAQ
Questions learners often ask
What does this PCDE question test?
Define data structures and implement SQL for Business Intelligence — This question tests Define data structures and implement SQL for Business Intelligence — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Add effective start and end date columns for each dimension attribute — Option B is correct because Type 2 SCD requires preserving full history by adding effective start and end date columns to the dimension table. This allows BI reports to join on a fact row's transaction timestamp and retrieve the exact dimension attribute values that were current at that point in time, ensuring historical accuracy without data loss.
What should I do if I get this PCDE 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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Last reviewed: Jul 4, 2026
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