DA0-002 Data Acquisition and Preparation Practice Question
An analyst needs to compute a running total of sales for each department, ordered by date. Which window function is most appropriate?
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
✓
SUM(sales) OVER (PARTITION BY department ORDER BY date)
SUM() with OVER(PARTITION BY department ORDER BY date) computes a running total within each department.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
ROW_NUMBER() OVER (PARTITION BY department ORDER BY date)
Why it's wrong here
ROW_NUMBER() assigns a sequential number, not a running total.
- ✗
SUM(sales) OVER (ORDER BY date)
Why it's wrong here
This gives a running total across all departments, not per department.
- ✓
SUM(sales) OVER (PARTITION BY department ORDER BY date)
Why this is correct
Partitions by department and orders by date to compute running total per department.
- ✗
LAG(sales, 1) OVER (PARTITION BY department ORDER BY date)
Why it's wrong here
LAG gives the previous value, not a running total.
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