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Given a table sales with column amount containing values (100, NULL, 200, NULL, 300), what is the result of SELECT SUM(amount) FROM sales;?

medium📝 query result Q4 of 15
SQL - Aggregate Functions
Given a table sales with column amount containing values (100, NULL, 200, NULL, 300), what is the result of SELECT SUM(amount) FROM sales;?
ANULL
B600
C100
D0
Step-by-Step Solution
Solution:

  1. Step 1: Understand SUM behavior with NULLs

    SUM ignores NULL values and sums only non-NULL amounts: 100 + 200 + 300 = 600.

  2. Step 2: Confirm no NULL affects the sum

    NULLs do not add or cause NULL result in SUM.

  3. Final Answer:

    600 -> Option B

  4. Quick Check:

    SUM ignores NULLs and sums non-NULL values = A [OK]
Quick Trick: SUM skips NULLs, sums only actual numbers [OK]
Common Mistakes:
MISTAKES
  • Assuming SUM returns NULL if any NULL exists
  • Counting NULL as zero automatically
  • Confusing SUM with COUNT

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