[Solved] Why does using multiple LEFT JOIN clauses sometimes cause unexpected NULLs in the result? — Ans: Because each LEFT JOIN adds NULLs when no matching rows exist in the joined... | SQL

SQL - LEFT and RIGHT JOIN

Why does using multiple LEFT JOIN clauses sometimes cause unexpected NULLs in the result?

ABecause each LEFT JOIN adds NULLs when no matching rows exist in the joined table.

BBecause LEFT JOIN removes rows without matches, causing NULLs.

CBecause LEFT JOIN duplicates rows when matches exist.

DBecause LEFT JOIN only returns rows with matches in all tables.

Step-by-Step Solution

Solution:

Step 1: Understand LEFT JOIN NULL behavior
LEFT JOIN returns all rows from the left table and fills NULLs for missing matches in the right table.
Step 2: Apply to multiple LEFT JOINs
Each LEFT JOIN can add NULLs independently if no matching rows exist in that joined table.
Final Answer:
Because each LEFT JOIN adds NULLs when no matching rows exist in the joined table. -> Option A
Quick Check:
LEFT JOIN NULL fill = Because each LEFT JOIN adds NULLs when no matching rows exist in the joined table. [OK]

Quick Trick: Each LEFT JOIN adds NULLs if no match found [OK]

Common Mistakes:

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Why does using multiple LEFT JOIN clauses sometimes cause unexpected NULLs in the result?