Warn user if they @select a column which doesn't exist

[metanoid]

If the user specifies named columns to @select, and any of those columns do not exist, the macro does not provide a warning.

For example, I wanted to get two named columns from a DataFrame called df:

df |> @select(:first_col, :secon_col) # note mis-spelling of `second_col`

Actual behaviour:
This returned a query result with only first_col.
Expected behaviour:
Show a warning like No column "secon_col" in source, and then return a query result with only first_col

[davidanthoff]

I think we could even throw an error in this case.

[AliMalik9599]

Hi @davidanthoff I am interested in working on this issue if it has not been completed already. Any advice on getting started? I am thinking of just displaying a warning message as long as one of the arguments is valid. Thanks for the help!