IPS v4 upgrade -- DB issues

[InsanityScreams]

Apologies for creating another topic -- I'm running into a few issues whilst testing upgrading our forum to IPSv4.

When I try to run the first sql query manually (to change 'current_controller' in *_core_sessions) I receive an error because the column doesn't exist (in fact it looks like the table doesn't exist at this point). Oddly, if I choose to try and run it automagically then the upgrader doesn't throw up any issues. I can run other queries manually and successfully.

1) Does anybody have any suggestions as to what might be causing this?

2) Also can somebody suggest why after a successful upgrade to v4 my database is literally half the size that it started with (about 3GB instead of 6GB)? What is being stripped/compressed to achieve this -- that's rather a drastic change...!

[InsanityScreams]

Correction (sorry) -- the table does exist, but the column does not.  The specific query is:

ALTER TABLE `ibf_core_sessions` CHANGE COLUMN `current_controller` `current_controller` VARCHAR (100) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT '' COMMENT '';

I can't seem to find where this column should have been created -- I'd really appreciate any pointers?