Solution:Step 1: Analyze the WHERE clause conditionThe condition price > 0 excludes prices equal to zero, so only prices greater than zero are included.Step 2: Consider data and NULL resultIf no prices are greater than zero, the filtered set is empty, so AVG() returns NULL.Final Answer:The WHERE cla

[Solved] Consider this query:SELECT AVG(price) FROM Products WHERE price > 0;It returns NULL even though there are products with price 0 and above. What is the likely problem? | SQL

SQL - Aggregate Functions

Consider this query:
SELECT AVG(price) FROM Products WHERE price > 0;
It returns NULL even though there are products with price 0 and above. What is the likely problem?

AThe WHERE clause excludes all rows because price > 0 filters out zero prices

BAVG() cannot be used with WHERE clause

CThe price column contains only NULL values

DAVG() requires GROUP BY to work

Step-by-Step Solution

Solution:

Step 1: Analyze the WHERE clause condition
The condition price > 0 excludes prices equal to zero, so only prices greater than zero are included.
Step 2: Consider data and NULL result
If no prices are greater than zero, the filtered set is empty, so AVG() returns NULL.
Final Answer:
The WHERE clause excludes all rows because price > 0 filters out zero prices -> Option A
Quick Check:
Empty filtered rows cause AVG() to return NULL [OK]

Quick Trick: Check WHERE filters exclude all rows causing NULL AVG() [OK]

Common Mistakes:

MISTAKES

Thinking AVG() can't use WHERE
Assuming AVG() needs GROUP BY always
Ignoring that empty sets return NULL

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Consider this query:

Step 1: Analyze the WHERE clause condition

Step 2: Consider data and NULL result

Final Answer:

Quick Check:

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