Why does a LEFT JOIN sometimes behave like an INNER JOIN when a WHERE clause filters on the right table columns?

hard📝 Conceptual Q10 of 15

SQL - LEFT and RIGHT JOIN

Why does a LEFT JOIN sometimes behave like an INNER JOIN when a WHERE clause filters on the right table columns?

ABecause LEFT JOIN automatically converts to INNER JOIN with WHERE

BBecause the WHERE clause excludes rows where right table columns are NULL

CBecause ON clause is ignored when WHERE is present

DBecause LEFT JOIN only preserves rows with matching right table rows

Step-by-Step Solution

Solution:

Step 1: Understand LEFT JOIN and NULLs
LEFT JOIN includes all left rows; unmatched right rows have NULLs in right columns.
Step 2: Effect of WHERE on right table columns
WHERE filters out rows where right columns are NULL, removing unmatched left rows.
Final Answer:
Because the WHERE clause excludes rows where right table columns are NULL -> Option B
Quick Check:
WHERE on right columns can turn LEFT JOIN into INNER JOIN effect [OK]

Quick Trick: WHERE on right table columns removes NULLs, mimicking INNER JOIN [OK]

Common Mistakes:

MISTAKES

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