Table definitions, including fields names, are /not/ to be
played with lightly in a functioning relational database system. Within
any non-trivial system there will be many very carefully designed 'relations'
(hence the name: relational database) between tables and the slightest change
to any of these, which certainly includes changing a field name, is very likely
to affect the functioning of the whole system, usually breaking it. Such
changes should only be done with an in-depth knowledge of the database design
and substantial understanding of how relational databases work and of
programming (in this case in PHP).
A database administrator tool (such as the module you mention) is a very
powerful tool for a database designer /developer / programmer and I'd go as far
as to suggest that you should /never/ use it to change data unless you know
/exactly/ what the consequences will be, probably after having studied and
understood substantial parts of the PHP code that runs Moodle.
The best you can do now is probably to rename the field back straight away and
keep your fingers crossed that no widespread damage has been done meanwhile by
other PHP code responding to the change you made. If you're very lucky,
everything will work again. This will be very much influenced by whether
anyone (including yourself) has tried to update any data while the field was
I would then have a good look around the system, especially
parts connected with what you were trying to change (user information) to look
for signs of whether anything appears not to be working as expected. This
will be a bit hit-or-miss (unless you are going to invest a /lot/ of time in
understanding the relational model used in Moodle) but will hopefully identify
any major problems.
In general, it is relatively 'safe' to add a new field to a table (since that
will not break any existing relations / structure) but highly dangerous to change an
existing field definition in any way without a lot of meticulous checking of
the underlying relations and code. The smallest change to the structure
of a relational database is a highly technical process in which it is easy to
do great damage unless you have considerable experience and have done a lot of
preparatory work, including thorough familiarisation with all the ways any
changed fields are used throughout the system. In fact adding a new field
is probably pointless unless you are prepared to get your hands dirty with a
/lot/ of checking and cross-checking of the developer documentation and are
going to be writing significant PHP code.
Sorry if some of this is familiar ground or sounds a bit heavy, but it's hard
to over-emphasise the damage that can be done to a database by even the tiniest
of 'inappropriate' changes - it's very different from something like Word or
Excel in this respect... you can't count on just experimenting with a little
change and keeping your fingers crossed in the knowledge that you can undo
it... by the time you try to undo the change its effects could have propogated widely
within the database if there has been any other access to it by any process
If after reverting the change of field name things don't appear to be working
properly your only option will probably be to restore the database
itself. In fact, from a technical point of view, unless you can guarantee
that no other data change might have taken place, restoring the database is the
only really safe way to get back to a working system.
So, try to change it back and good luck. If you really want to make such
a change spend a /lot/ of time studying the developer documentation and existing
PHP code first.