SQL - CASE Expressions
Which of the following is the correct syntax to count rows where
score is greater than 50 using CASE inside COUNT?Which of the following is the correct syntax to count rows where score is greater than 50 using CASE inside COUNT?
easy📝 Syntax Q12 of 15
Step-by-Step Solution
Solution:
Step 1: Recall COUNT counts non-null values
COUNT counts rows where expression is NOT NULL.Step 2: Use CASE to return 1 for matches, NULL otherwise
CASE WHEN condition THEN 1 END returns 1 or NULL (default ELSE NULL).Final Answer:
SELECT COUNT(CASE WHEN score > 50 THEN 1 END) FROM results; -> Option AQuick Check:
COUNT with CASE returning NULL for no match counts only matches [OK]
Quick Trick: COUNT counts non-null, so ELSE NULL is default [OK]
Common Mistakes:
- Using ELSE 0 causes COUNT to count all rows
- Omitting WHEN keyword
- Using invalid CASE syntax
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