SQL - Window Functions Fundamentals
Why does the
PARTITION BY clause inside the OVER clause not reduce the number of rows returned by a query?Why does the PARTITION BY clause inside the OVER clause not reduce the number of rows returned by a query?
hard📝 Conceptual Q10 of 15
Step-by-Step Solution
Solution:
Step 1: Understand the effect of PARTITION BY on rows
PARTITION BY groups rows logically for window functions but does not remove or filter any rows.Step 2: Differentiate from filtering or sorting
Filtering is done by WHERE, sorting by ORDER BY; PARTITION BY only defines groups for calculations.Final Answer:
Because PARTITION BY divides rows into groups but does not aggregate or filter rows -> Option AQuick Check:
PARTITION BY groups rows, does not reduce row count [OK]
Quick Trick: PARTITION BY groups rows, does not filter or reduce them [OK]
Common Mistakes:
- Thinking PARTITION BY filters rows
- Confusing PARTITION BY with GROUP BY
- Assuming PARTITION BY sorts rows
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