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Introduction
4. Purpose of functions
Summary

## Instruction

What are the benefits of using functions? Let's list the main advantages:

• Functions extend the functionality of a database (we are allowed to add custom functions).
• A function allows you to encapsulate logic that can be invoked like a programming subroutine.
• Code reusability. Imagine that we have to repeat some calculations in our SQL queries. It would be tedious to manually hard-code these calculations. Instead, we can simply create a generic function that takes some inputs and performs the calculations for us.

Warning (portability): each database engine (for instance Oracle, SQL Server, etc.) has slightly different syntax for creating functions, though the concepts are similar in all database engines.

## Exercise

Select the id, radius, diameter, and computed circumference and area of each record from the circle table (using our newly-created get_pi() function).

Note:

• The circumference of a circle equals pi * diameter.
• The area of a circle equals pi * radius * radius.

Mind the order of multiplying – it matters when it comes to SQL and floating-point numbers.