Can you explain what an aggregate function is and what it is used for in databases?

An aggregate function in databases is a function that takes a set of values and returns a single value that summarizes or consolidates this data. It is used for calculating statistics or summary data.

Examples of aggregate functions:

• COUNT() — counts the number of rows
• SUM() — sums the values
• AVG() — calculates the average
• MAX() and MIN() — find the maximum and minimum values respectively

Aggregate functions are often used together with the GROUP BY operator to obtain summary data by groups, such as the number of orders per customer or the average income per month.