How to design a database for User Defined Fields?

Question

My requirements are:

• Need to be able to dynamically add User-Defined fields of any data type
• Need to be able to query UDFs quickly
• Need to be

Answer 1

Even if you provide for a user adding custom columns, it will not necessarily be the case that querying on those columns will perform well. There are many aspects that go into query design that allow them to perform well, the most important of which is the proper specification on what should be stored in the first place. Thus, fundamentally, is it that you want to allow users to create schema without thought as to specifications and be able to quickly derive information from that schema? If so, then it is unlikley that any such solution will scale well especially if you want to allow the user to do numerical analysis on the data.

Option 1

IMO this approach gives you schema with no knowledge as to what the schema means which is a recipe for disaster and a nightmare for report designers. I.e., you must have the meta data to know what column stores what data. If that metadata gets messed up, it has the potential to hose your data. Plus, it makes it easy to put the wrong data in the wrong column. ("What? String1 contains the name of convents? I thought it was Chalie Sheen's favorite drugs.")

Option 3,4,5

IMO, requirements 2, 3, and 4 eliminate any variation of an EAV. If you need to query, sort or do calculations on this data, then an EAV is Cthulhu's dream and your development team's and DBA's nightmare. EAV's will create a bottleneck in terms of performance and will not give you the data integrity you need to quickly get to the information you want. Queries will quickly turn to crosstab Gordian knots.

Option 2,6

That really leaves one choice: gather specifications and then build out the schema.

If the client wants the best performance on data they wish to store, then they need to go through the process of working with a developer to understand their needs so that it is stored as efficiently as possible. It could still be stored in a table separate from the rest of the tables with code that dynamically builds a form based on the schema of the table. If you have a database that allows for extended properties on columns, you could even use those to help the form builder use nice labels, tooltips etc. so that all that was necessary is to add the schema. Either way, to build and run reports efficiently, the data needs to be stored properly. If the data in question will have lots of nulls, some databases have the ability to store that type of information. For example, SQL Server 2008 has a feature called Sparse Columns specifically for data with lots of nulls.

If this were only a bag of data on which no analysis, filtering, or sorting was to be done, I'd say some variation of an EAV might do the trick. However, given your requirements, the most efficient solution will be to get the proper specifications even if you store these new columns in separate tables and build forms dynamically off those tables.

Sparse Columns