[Solved] Given the table sales with rows:id | amount1 | 102 | 203 | 15What is the output of this query?SELECT id, amount, (SELECT SUM(amount) FROM sales WHERE id | SQL

SQL - Advanced Query Patterns

Given the table sales with rows:

id | amount
1  | 10
2  | 20
3  | 15

What is the output of this query?

SELECT id, amount, (SELECT SUM(amount) FROM sales WHERE id <= s.id) AS running_total FROM sales s ORDER BY id;

A1 | 10 | 10 2 | 20 | 20 3 | 15 | 15

B1 | 10 | 10 2 | 20 | 30 3 | 15 | 45

C1 | 10 | 10 2 | 20 | 25 3 | 15 | 40

D1 | 10 | 10 2 | 20 | 30 3 | 15 | 15

Step-by-Step Solution

Solution:

Step 1: Calculate running total for each row
For id=1: sum amounts where id <=1 is 10.
For id=2: sum amounts where id <=2 is 10+20=30.
For id=3: sum amounts where id <=3 is 10+20+15=45.
Step 2: Match calculated values with options
1 | 10 | 10
2 | 20 | 30
3 | 15 | 45 matches these running totals exactly.
Final Answer:
1 | 10 | 10
2 | 20 | 30
3 | 15 | 45 -> Option B
Quick Check:
Running total sums all previous rows [OK]

Quick Trick: Add amounts cumulatively by id order [OK]

Common Mistakes:

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