ZNC's primary code does not yet have the ability to log accounts on join, but there is a (simple) patch that adds it to the end of the Joins line, so now we can pick that data up.  It is of course optional, if the new account information is not available everything works fine.

There is more to do for querydb.pl but this collects the data and allows
basic queries.

You will need to update your database regardless.  Depending upon how large your database is this can take a lot of time, so disable any update cronjobs.  Update your table references to the correct ones of course.

alter table chatdb_sphinx add account varchar(40) after network;

CREATE INDEX accountidx on chatdb_sphinx (account)

Also some small tweaks around showing the highlight on the dates and a
fix to not query the entire database by accident, such as not quoting
the channel name and winding up with no actual arguments.