✅ Aggregate functions are special SQL functions that:

Take multiple input values (from rows) and return a single value as a summary.

• They work on a set of rows — not just one row at a time.
• Used commonly with GROUP BY to summarize data.

Common Aggregate Functions

Function	What It Does
COUNT()	Counts the number of rows.
SUM()	Adds up values.
AVG()	Calculates the average (mean) value.
MIN()	Finds the minimum value.
MAX()	Finds the maximum value.

Quick Examples

Assume a table Sales:

sale_id	amount
1	100
2	150
3	200

1. COUNT()

Count how many sales there are:

SELECT COUNT(*) FROM Sales;

Result: 3

2. SUM()

Total sales amount:

SELECT SUM(amount) FROM Sales;

Result: 450 (100 + 150 + 200)

3. AVG()

Average sale amount:

SELECT AVG(amount) FROM Sales;

Result: 150.00

4. MIN()

Smallest sale:

SELECT MIN(amount) FROM Sales;

Result: 100

5. MAX()

Largest sale:

SELECT MAX(amount) FROM Sales;

Result: 200

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Other Useful Aggregate Functions

Function	Description
COUNT(DISTINCT col)	Count unique values only.
GROUP_CONCAT(col) (MySQL)	Concatenates values into a string (e.g., "A,B,C")
STRING_AGG(col, ', ') (PostgreSQL, SQL Server)	Newer SQL standard for string concatenation.
VAR_SAMP() / STDDEV()	Variance / standard deviation for statistical summaries.

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Where Are Aggregate Functions Commonly Used?

• GROUP BY summaries:

SELECT department, SUM(salary)
FROM Employees
GROUP BY department;

• Reports — totals, averages, counts.
• Data analytics — distributions, trends.

In Short

Aggregate functions summarize multiple rows into a single result — essential for reporting, analytics, and grouped summaries.