Support for dropping columns from a database

[tdimitrov]

It would be really nice to have support for dropping arbitrary (or just the last) column from a Database instance.

[cheme]

Do you need to change the options of the drop column?

[tdimitrov]

Do you need to change the options of the drop column?

Probably stupid question, but why would I want to change the options of a column which is going away?

[cheme]

you can have an ordered indexed column and switch to non ordered one, or on hash indexed use preimage or something else, I think I will implement an optional change (make sense to me to have it).

[arkpar]

@cheme Changing these options while preserving data is out of scope of this issue. As for the case when loosing data isacceptable, we already have add_column. So remove_column followed by add_column should be enough.

[arkpar]

What kind of "drop" is expected here? Removing a column entirely (and shifting following column indicies)? Or simply clearing all data?

[cheme]

I am implementing a full removal (remove at file level, so it is simple to reset different option).
With no indices shift.

[arkpar]

I think proper behaviour for actually removing a column would be to shift following columns and rename their files.
As @tdimitrov suggested, we can just support removing the last column for now. In which case there's no need to rename/move anything.

[cheme]

I don t know if the shift could not be something that force user to manage two set of column index so a bit of additional work for him.
Maybe providing an api to move column would work Db::move_column(options, from, to). This way the shift is at convenience of the user.

[tdimitrov]

you can have an ordered indexed column and switch to non ordered one, or on hash indexed use preimage or something else, I think I will implement an optional change (make sense to me to have it).

No. For my particular case - I want to drop all the data and remove the column from the metadata.

Removing any column would be nice. drop_last + move_column is also acceptable.