[Solved] Identify the error in this SQL query using multiple LEFT JOINs:SELECT a.id, b.name, c.status FROM tableA a LEFT JOIN tableB b ON a.id = b.a_id LEFT JOIN tableC c ON b.id = c.b_id WHERE c.... | SQL

SQL - LEFT and RIGHT JOIN

Identify the error in this SQL query using multiple LEFT JOINs:

SELECT a.id, b.name, c.status FROM tableA a LEFT JOIN tableB b ON a.id = b.a_id LEFT JOIN tableC c ON b.id = c.b_id WHERE c.status = 'active';

AThe SELECT clause must include all columns from joined tables

BThe JOIN conditions are missing ON clauses

CUsing LEFT JOIN twice is not allowed

DThe WHERE clause filters out rows where c.status is NULL, negating LEFT JOIN effect

Step-by-Step Solution

Solution:

Step 1: Understand WHERE with LEFT JOIN
The WHERE clause filters rows after JOINs. Filtering on c.status excludes rows where c is NULL, removing unmatched rows.
Step 2: Effect on LEFT JOIN
This makes the LEFT JOIN behave like INNER JOIN, losing rows from tableA without matching tableC rows.
Final Answer:
The WHERE clause filters out rows where c.status is NULL, negating LEFT JOIN effect -> Option D
Quick Check:
Filtering on joined table in WHERE breaks LEFT JOIN [OK]

Quick Trick: Use WHERE on main table only; filter joined tables in ON [OK]

Common Mistakes:

MISTAKES

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Identify the error in this SQL query using multiple LEFT JOINs: