[Solved] Consider this query intended to calculate a running total:SELECT id, amount, (SELECT SUM(amount) FROM sales WHERE id What is the main issue with this query? | SQL

SQL - Advanced Query Patterns

Consider this query intended to calculate a running total:

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

What is the main issue with this query?

AIt will cause a syntax error due to missing GROUP BY.

BIt uses window functions which are not allowed.

CIt excludes the current row's amount from the running total.

DIt sums amounts from unrelated tables.

Step-by-Step Solution

Solution:

Step 1: Analyze the subquery condition
The subquery sums amounts where id is less than current row's id, so it excludes the current row's amount.
Step 2: Understand running total definition
Running total should include the current row's amount, so condition should be id <= s.id, not id < s.id.
Final Answer:
It excludes the current row's amount from the running total. -> Option C
Quick Check:
Use id <= current id to include current row [OK]

Quick Trick: Check if current row is included in sum condition [OK]

Common Mistakes:

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