DA0-002 Data Concepts and Environments Practice Question
A company's database has a table 'orders' with columns: order_id, customer_id, order_date, and total_amount. A data analyst needs to identify customers who have placed more than 5 orders in the past year. Which data concept should be used to group orders by customer and count them?
⚠ Common exam trap
Many exam-takers confuse filtering (WHERE) with aggregation (GROUP BY), thinking that a WHERE clause alone can count orders per customer, when in fact WHERE only filters rows and cannot produce grouped counts.
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
✓
Aggregation with GROUP BY
The requirement to count orders per customer requires grouping rows by customer_id and then applying a count function. The GROUP BY clause in SQL aggregates rows that share a common value (customer_id) into summary rows, and the COUNT function tallies the number of orders per group. This is the standard approach for such 'per-customer' aggregations.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Joining with other tables
Why it's wrong here
Joining combines tables, not needed here.
- ✗
Filtering with WHERE clause
Why it's wrong here
Filtering selects rows, does not group.
- ✗
Sorting with ORDER BY
Why it's wrong here
Sorting orders results, does not group.
- ✓
Aggregation with GROUP BY
Why this is correct
GROUP BY groups rows and aggregation functions compute counts.
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