Why does a LEFT JOIN sometimes return NULL values in the right table columns even when the join condition seems correct?

hard📝 Conceptual Q10 of 15

SQL - LEFT and RIGHT JOIN

Why does a LEFT JOIN sometimes return NULL values in the right table columns even when the join condition seems correct?

ABecause no matching row exists in the right table for that left row

BBecause LEFT JOIN always returns NULLs for right table

CBecause the join condition is ignored in LEFT JOIN

DBecause the right table is empty

Step-by-Step Solution

Solution:

Step 1: Understand LEFT JOIN behavior
LEFT JOIN returns all left rows; if no matching right row, right columns are NULL.
Step 2: Reason about NULLs in right columns
NULLs appear only when no matching right row satisfies the join condition.
Final Answer:
Because no matching row exists in the right table for that left row -> Option A
Quick Check:
NULLs in right columns = no match found [OK]

Quick Trick: NULLs in right table columns mean no matching right row [OK]

Common Mistakes:

MISTAKES

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