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Which SQL expression correctly replaces NULL values with zero before summing a column sales?

easy📝 Syntax Q12 of 15
SQL - Aggregate Functions
Which SQL expression correctly replaces NULL values with zero before summing a column sales?
ASUM(NULLIF(sales, 0))
BSUM(sales)
CSUM(COALESCE(sales, 0))
DSUM(ISNULL(sales))
Step-by-Step Solution
Solution:

  1. Step 1: Understand COALESCE usage

    COALESCE(sales, 0) replaces NULL values in sales with 0 before summing.

  2. Step 2: Check other options

    SUM(sales) ignores NULLs, NULLIF returns NULL if sales=0, ISNULL(sales) is incomplete syntax.

  3. Final Answer:

    SUM(COALESCE(sales, 0)) -> Option C

  4. Quick Check:

    Use COALESCE to replace NULLs before aggregation [OK]
Quick Trick: Use COALESCE(column, 0) to treat NULL as zero in sums [OK]
Common Mistakes:
MISTAKES
  • Using SUM(sales) and expecting NULLs counted as zero
  • Confusing NULLIF with COALESCE
  • Using ISNULL without second argument

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