Business rules are incredibly important to every organisation. They can be made application independent by placing them in a MySQL database.

When creating an application that uses business rules there is a very important point that a programmer should remember: the business rules should not be built into the application. Business rules should be made available to the application, but not hard coded into it. The reasons for this are:

1- business rules evolve
2- situations change (for example new regulations)
3- the business rules may be used by more that one application

The last thing that the programmer wants is to create new application releases every time that a business rule is added or updated. And that's where MySQL comes in.

![](https://steemitimages.com/DQmYusMopng4J59bibQEpb1HvxgF9kPJ9VoeccnW4xQS2d1/image.png)

<h3>MySQL and Business Rules</h3>

The aim of the business rule programmer is to create a two-tier application consisting of:

1- the business rule layer
2- the application layer

A MySQL database is an obvious choice for the business rule layer because it can be accessed from most programming languages and the programmer can:

1- store the business rule information in tables and/or
2- use stored stored functions to run the business rules (anyone unsure of how to create a MySQL stored function should read MySQL Stored Procedures and Functions)

By using a MySQL database the programmer can create a set of business rules that can be used by any application that needs to be developed, whether that be a desktop application (perhaps using C#, C++ or VB) or an Internet application (perhaps using .NET or PHP).


<h3>Creating a Simple MySQL Stored Function Business Rule</h3>

The business rules themselves can be built into a MySQL function. Obviously it may write to any database table as require, but at its simplest level it can just be a series of if..then..else statements. In this example the function returns the appropriate action depending on the input from the user:

<code>delimiter //
drop function if exists business_rule;
create function business_rule (status varchar(50)) returns varchar(50)
deterministic
begin
declare new_status varchar(50);
if status = "new" then
set new_status = "case opened - send to engineer";
elseif status = "fixed" then
set new_status = "problem solved - inform customer";
elseif status = "nofix" then
set new_status = "problem unresolved - sent to engineer";
elseif status = "raise" then
set new_status = "problem escalated - inform manager";
elseif status = "close" then
set new_status = "case closed";
else set status = "undefined";
end if;
return new_status;
end
//
delimiter ;</code>

This function can now be used as required by the programmer. For example it can be run from the command line (as shown in figure 1 at the bottom of this article):
<code>echo "select business_rule('new')" | mysql -uuser -ppassword business_rules_db</code>

Or it can be used in languages such as C#. But however the business rules are to be use the key things to remember are:

1- those business rules are now available to any programming language or application that can interface with a MySQL database
2- the business rules can be updated and added to without having to change the client application

And so, at the end of this process, the programmer will have a powerful and adaptable set of business rules that are independent of the application that will use them.

<br /><hr/><em>Posted on <a href="https://utopian.io/utopian-io/@haig/how-to-use-business-rules-in-a-mysql-database-using-mysql-functions-to-create-two-tier-business-savvy-applications">Utopian.io -  Rewarding Open Source Contributors</a></em><hr/>