This guide is specifically for PostgreSQL syntax.

SQL Aggregate Functions Cheat Sheet

Reference for COUNT, SUM, AVG, MIN, MAX and GROUP BY usage.

COUNT

Syntax:

COUNT(*) | COUNT(column) | COUNT(DISTINCT column)

Counts rows. COUNT(*) includes NULLs, COUNT(column) excludes NULLs.

Example:

SELECT COUNT(*) as total, COUNT(email) as with_email, COUNT(DISTINCT dept) as depts FROM users;

💡 Note: COUNT(1) = COUNT(*)

SUM

Syntax:

SUM(column) | SUM(DISTINCT column)

Adds up numeric values. Ignores NULLs.

Example:

SELECT SUM(amount) as total, SUM(DISTINCT amount) as unique_sum FROM transactions;

💡 Note: Returns NULL if all values are NULL

AVG

Syntax:

AVG(column) | AVG(DISTINCT column)

Calculates arithmetic mean. Ignores NULLs.

Example:

SELECT AVG(salary) as avg_salary, ROUND(AVG(salary), 2) as rounded FROM employees;

💡 Note: Use ROUND() for decimal precision

MIN / MAX

Syntax:

MIN(column) | MAX(column)

Finds minimum or maximum value. Works on numbers, strings, dates.

Example:

SELECT MIN(salary) as lowest, MAX(salary) as highest, MAX(hire_date) as newest FROM employees;

💡 Note: Works with any comparable type

GROUP BY

Syntax:

SELECT columns, AGG() FROM table GROUP BY columns

Groups rows by column values for aggregation.

Example:

SELECT department, AVG(salary) FROM employees GROUP BY department;

💡 Note: Non-aggregated columns must be in GROUP BY

HAVING

Syntax:

SELECT columns, AGG() FROM table GROUP BY columns HAVING condition

Filters groups after aggregation (WHERE filters before).

Example:

SELECT department, COUNT(*) FROM employees GROUP BY department HAVING COUNT(*) > 5;

💡 Note: Can use aggregate functions in HAVING

Quick Reference Table

| Function | Purpose | |----------|---------| | COUNT | Counts rows | | SUM | Adds up numeric values | | AVG | Calculates arithmetic mean | | MIN / MAX | Finds minimum or maximum value | | GROUP BY | Groups rows by column values for aggregation | | HAVING | Filters groups after aggregation (WHERE filters before) |

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PostgreSQL-Specific Notes

This page covers PostgreSQL syntax. Other databases may have different syntax for similar operations.