SQL aggregate functions (COUNT, SUM, AVG)

Code pattern

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Definition

Functions that calculate one value from many rows: COUNT (number), SUM (total), AVG (mean), MIN and MAX.

Example

SELECT AVG(mark) FROM results;

Found in: course specifications, 2025 HSC marking guidelines, school notes, past SDD papers.

Where you'll use it in the test

Syllabus area: Y12 Programming for the Web.

Question types it can appear in

SQL: Write or read it in the SQL query tool.
Fill in the blanks: Choose this term to complete a statement or table.
Code reading: Code or algorithm reading: interpret a fragment and state its output or purpose.

Where it has appeared in the paper

Programming for the Web (Part A, B). Part letters follow each paper’s own layout.

How to use it

A model sentence

General advice, built from the definition and example above

Code pattern: “Functions that calculate one value from many rows: COUNT (number), SUM (total), AVG (mean), MIN and MAX.” Then apply it: SELECT AVG(mark) FROM results;

In a short answer, give the definition in your own words first, then tie it to the situation in the question. Do not copy the example above unless it fits the scenario.

Official worked answer

2025 HSC Q21 (4 marks): SQL queries (4 marks): official criteria and sample answer

Criteria

4: Correct SQL query that extracts 'Pending' and 'Escalated' jobs for the 'Software' and 'Hardware' categories, counts the jobs for each status in each category, and outputs results in descending order. 3: Addresses most requirements. 2: Some understanding of the problem. 1: Some understanding of SQL or the problem.

Sample answer

SELECT Category, Status, COUNT(JobID) AS Jobs FROM Issues WHERE (Status = 'Pending' OR Status = 'Escalated') GROUP BY Status, Category ORDER BY Jobs DESC

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Go deeper

Flashcard: SQL aggregate functions (COUNT, SUM, AVG) in Programming for the Web (Year 12) · study that set
Memorise: SQL vs ORM
Full term page: every question, note and marking comment for SQL aggregate functions (COUNT, SUM, AVG)

Check yourself

Write or say the “SQL aggregate functions (COUNT, SUM, AVG)” pattern from memory: the syntax and what it does.

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