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These plan rewrite happens during the sql-to-rel conversion phrase.

Column Computation and Storage

For table scan, virtual column are computed from expression; stored column are queried from the real table source.

For table sink, virtual column is ignored; stored column is computed from expression when insert into sink.

The TableSchema Change

We would extend the TableSchema to support computed columns.(We should always keep one TableSchema in the code, in the future, connectors would only see the row type but not the TableSchema so we should not have this concern.)

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