[Solved] What will be the result of this query on table orders with columns order_id and price if order_id values are not unique?SELECT o1.order_id, o1.price, (SELECT SUM(o2.price) FROM orders o2 WHERE o2.... | SQL

SQL - Advanced Query Patterns

What will be the result of this query on table orders with columns order_id and price if order_id values are not unique?

SELECT o1.order_id, o1.price, (SELECT SUM(o2.price) FROM orders o2 WHERE o2.order_id <= o1.order_id) AS running_total FROM orders o1 ORDER BY o1.order_id;

AQuery will fail with syntax error because order_id is not unique.

BRunning totals may be incorrect due to duplicate order_id values causing sums to include multiple rows.

CRunning totals will be correct regardless of duplicate order_id values.

DQuery will return NULL for running_total when duplicates exist.

Step-by-Step Solution

Solution:

Step 1: Understand effect of duplicates in correlated subquery
The condition o2.order_id <= o1.order_id sums all rows with order_id less or equal, but duplicates cause repeated sums.
Step 2: Identify impact on running total
Duplicates cause running totals to be larger than expected because multiple rows share the same order_id and are summed multiple times.
Final Answer:
Running totals may be incorrect due to duplicate order_id values causing sums to include multiple rows. -> Option B
Quick Check:
Duplicates affect running total sums = Incorrect totals [OK]

Quick Trick: Ensure unique ordering column to avoid running total errors [OK]

Common Mistakes:

Assuming duplicates don't affect sums
Expecting syntax error on duplicates
Ignoring impact of non-unique keys

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What will be the result of this query on table orders with columns order_id and price if order_id values are not unique?

Step 1: Understand effect of duplicates in correlated subquery

Step 2: Identify impact on running total

Final Answer:

Quick Check:

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