# Aggregate Functions

Learn about SQL functions that take multiple values as input.

An **aggregate function** is a function that takes in multiple values and returns a single value. It can be viewed as a function that performs an operation over the values of multiple rows.

In T-SQL, we have these aggregate functions:

`AVG()`

: Returns the average of supplied values`COUNT()`

: Returns the number of rows`MIN()`

: Returns the minimum value`MAX()`

: Returns the maximum value`SUM()`

: Returns the sum

As an argument, all aggregate functions take an expression that returns a range of values. Often, the expression is the name of the column over the values of which we want to perform the operation:

```
SELECT AVG(ColumnName) AS Average
FROM TableSchema.TableName;
```

The `AVG()`

and `SUM()`

functions accept only numeric columns, while `MIN()`

, `MAX()`

, and `COUNT()`

functions can accept numbers, text, and datetime columns.

## Calculate the average

If we supply a range of numeric values, the `AVG()`

returns the average. We often use the `AVG()`

function to calculate the average of a particular column. Let’s calculate the average grade of students:

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