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Common exam pitfall
Students often confuse ASC (ascending/lowest first) with DESC (descending/highest first).
SELECT chooses fields, FROM chooses a table and WHERE filters records. ORDER BY sorts the resulting records. ASC sorts ascending; DESC sorts descending. Do not confuse sorting with filtering.
SELECT Name, Score
FROM Results
WHERE Score >= 50
ORDER BY Score DESC;Worked aggregates
Suppose three selected records have scores 4,7,9. SUM(Score) returns 20. COUNT(*) returns 3. These answer different questions: how much in total, and how many records. A WHERE condition can restrict which records contribute.
SELECT SUM(Score)
FROM Results
WHERE Team = 'Blue';For Blue scores 4 and 9 and a Red score 7, the filtered sum is 13. Do not add the Red score merely because it is in the same table.
Independent practice
Write a query counting all records, then change it to count only scores at least 50. Explain the difference between returning selected rows and returning one aggregate. GROUP BY and multi-table queries are optional extension and are not needed here.
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Exam-Style Check: Behavior of ORDER BY DESC in SQL
• Multiple ChoiceA school administrator runs the following SQL query on the Students table:
SELECT StudentName, ExamScore
FROM Students
ORDER BY ExamScore DESC;Which row will appear as the first result in the returned table?
Interactive exercises for Module 2 and beyond require an active plan.