**Aggregate -
Constituting or amounting to a whole**

Aggregate functions describe operations on
a set of values, like as counting, averaging, or finding minimum or maximum
values.aggregate functions to
assist with the restating of large volumes of data. The aggregate functions count`, sum`

`, avg`

`, max`

`, min`

```
and list not handle
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` NULL`

in the same way as ordinary functions and operators. Aggregate functions
perform a calculation on a set of values and return a single value.

Aggregate functions are used in the act of joining with a GROUP BY clause
to dispose values from a result set into groups.

There are some functions that operateon sets of values.

- MIN() and MAX() : find smallest and largest values.
- SUM() : summarize numeric values to produce sums (totals) .
- COUNT() : counts rows, values, or the number of distinct values.
- AVG() : calculate the average,used with numeric values.

Aggregate functions may be used with or without a GROUP BY clause that places rows into groups. Without a GROUP BY clause, an aggregate function calculates a summary value based on the entire set of selected rows. MySQL behaves with all the rows as a single group. With a GROUP BY clause, an aggregate function calculates a summary value for each group.

**MAX() and MIN( ) : **MAX function returns the
maximum and MIN function returns the minimum value of the set of values in
expression.

**For Example :** In the following example used a table 'clients' and used for max
and min function on the salary column of the table.

mysql> SELECT designation, MIN(salary),

MAX(salary) FROM clients GROUP BY designation;

**SUM() :** SUM function returns the sum of all
values in an expression.

**For Example : **For the clients table we have
apply the SUM function on the salary column and get total sum on salary.

mysql> select SUM(salary) FROM clients;

**COUNT( ) :** COUNT function returns the count
of the items in expression. The COUNT() function can be used in several ways to
count either rows or values.

**For Example :** It is used to find how many
clients , We have as follows.

mysql> select count(*) from clients;

**AVG( ) : **AVG is used to calculate average
value of an expression. It ignores NULL values.

For Example : We can use AVG function to calculate the average salary of all
clients buy executing the following query.

mysql> select avg<salary> from clients;