PCDE Practice Question: Define data structures and implement SQL for Business Intelligence
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 data analyst needs to create a rolling 30-day average of daily revenue. Which window function clause is required?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ROWS BETWEEN 29 PRECEDING AND CURRENT ROW
Option D is correct because `ROWS BETWEEN 29 PRECEDING AND CURRENT ROW` defines a physical window of exactly 30 rows (the current row plus the 29 preceding rows), which is the standard SQL approach for a rolling 30-day average when each row represents one day of revenue. This clause ensures that the window frame is fixed at 30 rows regardless of gaps in dates, making it reliable for daily data.
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.
✗
UNBOUNDED PRECEDING
Why it's wrong here
This includes all previous rows.
✗
RANGE BETWEEN INTERVAL 30 DAY PRECEDING AND CURRENT ROW
Why it's wrong here
This is valid but requires a date or timestamp column and may not guarantee exactly 30 rows if data is sparse.
✗
PARTITION BY month
Why it's wrong here
This partitions by calendar month, not a rolling window.
✓
ROWS BETWEEN 29 PRECEDING AND CURRENT ROW
Why this is correct
This selects exactly 30 rows (current + 29 preceding) for the rolling average.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between `ROWS` and `RANGE` window frames, where candidates mistakenly choose `RANGE` with an interval because it sounds more intuitive for date-based rolling averages, but the exam expects the precise `ROWS` syntax for a fixed row count.
Detailed technical explanation
How to think about this question
The `ROWS` clause defines a physical offset based on row position, which is deterministic and unaffected by gaps or duplicate dates in the data. In contrast, `RANGE` uses logical ordering based on the `ORDER BY` column values, which can lead to variable-sized windows if dates are not unique. For a rolling 30-day average on daily data, `ROWS BETWEEN 29 PRECEDING AND CURRENT ROW` is the safest choice because it guarantees exactly 30 rows per window, assuming one row per day. A real-world scenario where this matters is when a company has missing days (e.g., weekends or holidays) — `RANGE` would include more than 30 rows to cover 30 calendar days, while `ROWS` stays fixed at 30 rows, which may not align with the intended 30-day period.
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
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.
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: ROWS BETWEEN 29 PRECEDING AND CURRENT ROW — Option D is correct because `ROWS BETWEEN 29 PRECEDING AND CURRENT ROW` defines a physical window of exactly 30 rows (the current row plus the 29 preceding rows), which is the standard SQL approach for a rolling 30-day average when each row represents one day of revenue. This clause ensures that the window frame is fixed at 30 rows regardless of gaps in dates, making it reliable for daily data.
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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Question Discussion
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