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Why does COUNT(column_name) ignore NULL values internally in SQL?

hard📝 Conceptual Q10 of 15
SQL - Aggregate Functions
Why does COUNT(column_name) ignore NULL values internally in SQL?
ABecause NULL values are treated as zeros in COUNT
BBecause NULL values cause syntax errors in COUNT
CBecause COUNT(column_name) counts only unique values
DBecause NULL means unknown or missing, so it is excluded from counts
Step-by-Step Solution
Solution:

  1. Step 1: Understand NULL meaning

    NULL represents unknown or missing data, so it is not counted as a value.

  2. Step 2: Explain COUNT behavior

    COUNT(column_name) counts only known (non-NULL) values to give meaningful counts.

  3. Final Answer:

    Because NULL means unknown or missing, so it is excluded from counts -> Option D

  4. Quick Check:

    NULLs excluded because they represent missing data [OK]
Quick Trick: NULL means missing, so COUNT(column) skips it [OK]
Common Mistakes:
MISTAKES
  • Thinking NULL causes errors in COUNT
  • Assuming NULL counts as zero
  • Confusing COUNT(column) with COUNT(DISTINCT column)

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