Note I have updated the question with more info to explain why it is not a duplicate. Changes are in italics below.
I'm pretty new to Salesforce but come from a .NET/Sql Server background. So I am trying to understand how data is allocated in a Salesforce database (especially so since the standard size allocated to a database is really small compared to what I am used to.)
Basically what I want is a field in a table that is a textual description. It is something that the user can type in various notes, consequently, most of the time it is very short, a few dozen characters, but other times it can be extremely long -- 10,000 characters for example. I don't want to create a field that is 10,000 characters long, since that will quickly consume all the space.
n the databases I am used to you would create a field with a type where the space is shared -- varchar(max). These fields essentially have a big shared buffer of space so that each field is small but there is a large shared space that the field points in to.
I don't see anything like that in Salesforce, and, since it is such a common requirement, I was wondering what people recommend as the best approach to this so that I am not wasting loads of space for big, mostly empty fields.
Please note, this has been suggested as a duplicate -- however, my question refers to custom tables not the standard built in tables (as referenced in the putative duplicate.) How is the space calculated for a custom table. For example, if I want to store a table of "Notes" where are free form notes that can be any length from 0 to 20,000 characters. I don't want every row to take up 20,000 characters since most are very much shorter. I hope this clarifies my question, and I thank you in advance for your help.