Hi Li,

UDT is no replacement for a database, one reason why we renamed the module from User Defined Table to form and List.  The idea of a List is to show rich content directly to the user. The data itself should be part of the user experience, offering the ability to browse through the whole amount of records.

To answer your questions:

1. No, this requires a custom extension/ datatype. Even if that feature is asked several times, I don't think I will add that to the roadmap.
2. UDT uses a Regular expression on server side to validate the input.
3. Look up: A new datatype that looks up related information to other columns, for example size or nr. of downloads of a file inside a sownload column.
   Seperate: A none value datatype. Displays the column title and a horizontal line in edit mode, sepearting different sections of the input. Only visible in form/Edit mode
4. Each recors has a unique row id, you can show the value of it with a calulated column and the expression [UserDefinedRowId]
5. Performancce depends on number of cells and used datatypes. A url datatype is much more expensice than a simple text columns.
6. Not supported, sorry.

I made some tests with some thousands of records in one UDT, and it worked great. It depends really on the number of cells (columns x rows) and the used data types.
However, you can test the performance very quick.

Create your desired UDT and add one row, export UDT and edit the XML file. The row is listed there inside a <data> tag, copy that section 1000times, save and reimport. You might want to set debug=true inside web.config, otherwise your import might run into a time out. You can leave the import page after ckicking on Import, and you can watch your UDT growing using page refreshs. The whole import will run some minutes as "add" operations are most costly and require multiple sql database calls per row.