Datatable - adapter

In AppCode I call a Sql Database. I return DataAdapter - see attached file.
But how can I add a new column to the Adapter? Its value should be 2.
Thanks

public SqlDataAdapter GetTest()
    {
        SqlDataAdapter adapter = new SqlDataAdapter("TestSelect", connection);
        adapter.SelectCommand.CommandType = CommandType.StoredProcedure;
        return adapter;
    }

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