ExpressionEngine includes the ability to create your own custom fields; however, this ability is not limitless.  As you approach a few hundred custom fields, there is a minor possibility that your site will encounter a limit imposed by MySQL.  There is not a set limit to the total number of custom fields and the exact limit depends on several interacting factors.  There are a few symptoms that can help to identify when you have reached this limit:

MySQL Error:

MySQL ERROR:

Error Number: 1117

Description: Too many columns

or:

#1030 - Got error 139 from storage engine

If you encounter these symptoms, it is best to remove custom fields until the symptom is gone. 

In most cases where this many custom fields are used, there are better approaches to storing the data.  If you need assistance in discovering an approach that will work for your site, please post on the forums. 

There is no work-around for this MySQL limitation at this time.

For more information, please review this thread.