By default, set a column's type to "TEXT" if the format of data is wrong
I think we should, by default, set a column's type to "TEXT", if the format of data is wrong, instead of just emptying the column's content.
Rationale: if the format of the data you enter is wrong (e.g. improper decimal symbol), the number disappears without any warning. By default, the wrongly formatted data should be marked as "TEXT" type. Then, you could use the "Search&Replace" functionality to transfrom the data to a desired format, and then change the column's type.