[Solved] This query returns fewer rows than expected:SELECT C.Name, O.OrderID FROM Customers C LEFT JOIN Orders O ON C.ID = O.CustomerID AND O.Status = 'Completed';What is the likely problem? | SQL

SQL - LEFT and RIGHT JOIN

This query returns fewer rows than expected:
SELECT C.Name, O.OrderID FROM Customers C LEFT JOIN Orders O ON C.ID = O.CustomerID AND O.Status = 'Completed';
What is the likely problem?

ALEFT JOIN does not support multiple conditions

BO.Status column does not exist

CCustomers table is empty

DThe condition on O.Status in ON clause filters out unmatched rows

Step-by-Step Solution

Solution:

Step 1: Analyze ON clause with multiple conditions
Adding O.Status = 'Completed' in ON filters matches to only completed orders.
Step 2: Effect on LEFT JOIN
Rows with no completed orders get NULLs, but unmatched rows still appear; fewer matches reduce joined rows.
Final Answer:
The condition on O.Status in ON clause filters out unmatched rows -> Option D
Quick Check:
ON clause conditions limit matches in LEFT JOIN [OK]

Quick Trick: Conditions in ON limit matches; use WHERE for filtering results [OK]

Common Mistakes:

MISTAKES

Thinking LEFT JOIN ignores ON conditions
Assuming multiple ON conditions cause errors
Confusing ON and WHERE clauses

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This query returns fewer rows than expected:

Step 1: Analyze ON clause with multiple conditions

Step 2: Effect on LEFT JOIN

Final Answer:

Quick Check:

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