I was struggling with adding a computed column to an existing system-versioned table. In case anyone else with a similar problem lands here, I finally realized that the history table doesn't treat the column the same way. It ends up being similar to having an IDENTITY column on the base table, but that would result in a regular INT field on the history table.

If you are attempting to add a computed column to a system-versioned (temporal) table:

• First turn off system versioning
• Then add your computed column to the base table
• Verify the "type" of the resulting computed column
• Add the column with the appropriate static type to the history table
• Turn system versioning back on (DO NOT FORGET TO SPECIFY THE HISTORY TABLE)

I find it rather odd that you can accidentally omit the history_table when turning system versioning back on. I'd expect either it would resume versioning to the same table OR throw some kind of error considering it might be a bit unexpected behavior.

@pasquale-ceglie - I don't have enough reputation to comment, but I wanted to expand on what you said. You should be able to use most computed columns with temporal tables, just more manually. Basically you can't copy the schema definition with the computed columns, you can however replicate the resulting columns and generate the appropriate history table before trying to turn everything on. The definitions are just a bit different between the two tables (was quite confusing to me at first). I subscribed here, ping me if the above isn't clear and are curious.

System-versioned table schema modification fail because adding computed column while system-versioning is ON is not supported, so for the same reason you can't transform a regular table into a temporal one if there are computed columns on it.

Hope will help,