Identify the error in this query that tries to count all rows including NULLs in score column:

medium📝 Debug Q14 of 15

SQL - Aggregate Functions

Identify the error in this query that tries to count all rows including NULLs in score column:

SELECT COUNT(score) + COUNT(NULL) FROM results;

AThe query sums counts correctly

BCOUNT(score) counts all rows including NULLs

CCOUNT(NULL) counts NULLs as 1

DCOUNT(NULL) returns 0

Step-by-Step Solution

Solution:

Step 1: Understand COUNT(NULL) behavior
COUNT(NULL) always returns 0 because the NULL expression is always NULL and thus never counted.
Step 2: Analyze COUNT(score)
COUNT(score) counts only non-NULL values in score column, not all rows.
Final Answer:
COUNT(NULL) returns 0 -> Option D
Quick Check:
COUNT(NULL) always returns 0 [OK]

Quick Trick: COUNT(NULL) always returns zero, use COUNT(*) for all rows [OK]

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