Comments - Generated (Virtual and Persistent/Stored) Columns
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from this KB: "ALTER TABLE's MODIFY and CHANGE clauses are supported for PERSISTENT columns, but not for VIRTUAL columns."
I somehow understood that phrase to mean "no alter table for the virtual column once the virtual column is established"
I was trying to modify a "regular" column (which, further, had never contained any data) into a virtual one which in my opinion meant I was not modifying the virtual column (it was not yet "virtual"!). This did NOT work. Dropping my column and making a virtual column during the "first go round" works brilliantly.
Perhaps the "alter table" information in the KB could be made clearer. i.e. "Existing columns can not be altered into virtual columns."
Interestingly, the expression clause for virtual columns CAN be altered -- that is what I thought you had only one chance at . . .