Solution:Step 1: Understand LEFT JOIN and WHERE conditionThe LEFT JOIN keeps all A rows; WHERE b.value IS NULL filters unmatched B rows.Step 2: Interpret the resultThis query returns A rows without matching B rows.Final Answer:Find rows in A with no matching row in B -> Option AQuick Check:LEFT JOI

[Solved] Given the query:SELECT a.id, b.value FROM A a LEFT JOIN B b ON a.id = b.a_id WHERE b.value IS NULL;What is the likely purpose of this query? | SQL

SQL - LEFT and RIGHT JOIN

Given the query:
SELECT a.id, b.value FROM A a LEFT JOIN B b ON a.id = b.a_id WHERE b.value IS NULL;
What is the likely purpose of this query?

AFind rows in A with no matching row in B

BFind rows in B with no matching row in A

CFind all rows where b.value is NULL in both tables

DCause an error due to NULL comparison

Step-by-Step Solution

Solution:

Step 1: Understand LEFT JOIN and WHERE condition
The LEFT JOIN keeps all A rows; WHERE b.value IS NULL filters unmatched B rows.
Step 2: Interpret the result
This query returns A rows without matching B rows.
Final Answer:
Find rows in A with no matching row in B -> Option A
Quick Check:
LEFT JOIN + WHERE b.value IS NULL finds unmatched left rows [OK]

Quick Trick: WHERE right column IS NULL after LEFT JOIN finds unmatched left rows [OK]

Common Mistakes:

MISTAKES

Thinking it finds unmatched right rows
Assuming NULL comparison causes error
Confusing which table is left or right

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Given the query:

Step 1: Understand LEFT JOIN and WHERE condition

Step 2: Interpret the result

Final Answer:

Quick Check:

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