SQL Ordering & Aggregate Functions (ORDER BY, SUM, COUNT)

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.